Precise information for measuring masses and quantities for chemistry practical.

QUANTITIES AND MASSES

Chemists have balances for determining mass in grams or kilograms. They have graduated glassware for measuring the volumes of liquids and gases. There is, however, no simple measuring instrument for determining chemical amounts directly. Instead chemists first measure masses or volumes and then calculate the chemical amount.

Masses of chemicals and amounts in moles.

The most direct way to find amount of substances to weigh it on balance.

Amounts of substances/mol =( Mass of substances/g)/ (molar mass / g ^ mol)

This relationship gives rearrange to:

Mss of substance/g = (amounts of substances/mol) *( molar mass / g ^mol)

NOTE:Include the units in relationship and use them to check that the units on both sides equal sign are consistent.

Quantities of gases.

If the temperature and pressure are fixed, then the volume of a gas depends only on the amounts of gas in nmoles. In other words the volumes of a gas is determined by the number of gas molecules present.

The law applies so long as the molecules of a gas are so far apart that their volume is insignificant compared to the volume of the gas and so long as the intermolecular forces can be ignored. For many common gases these criteria apply under normal laboratory conditions. Under conditions where the gas is close liquefying the simple rules do not apply.

Avogadro's law follows from the ideal gas conditions:

pV=nRT ( where,R is the gas constant )

If p and T are constant, the volume is proportional to n, the amounts of gas in moles.

The molar volumes of a gas is the volume of 1 mole of the gas. when n=1

p=(RT/V)

substituting in this relationship gives for the molar volumes of any gases which behaves like an ideal gas. Two sets of conditions are commonly used for comparing amounts of gases:

• For accurate work the quantities are calculated or standard temperature and pressure,s.t.p. The standard temperature for gases is 273 K and the standard pressure is 101.3 kPa(1 atmosphere). Under these conditions the molar volumes of gas is 22400 cm^3
• For approximate work, when making estimates under laboratory conditions it is often convenient to use the fact the molar volume of a gas at around 20 degree celsius and 1 atmosphere pressure is about 24000 cm^3.

Amount of gas/ mol= (volume of gas/cm)/(molar volume/cm mol)

NOTE:Avogadro's law states that the equal volumes of gases contain equal amount of gas molecules, in moles, under the same conditions of temperature and pressure.

Quantities in solution Chemists measure the concentration of solution in moles per litre:

concentration/mol/dm^3= (amounts of solute/ mol )/ (volume of solution/ dm^3)

This rearranges to give:

amount of solute/mol= (volume of substances/dm^3) *( concentration /mol /Dm^3)

NOTE: A litre is cubic decimetre, dm^3.

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IMPORTANT INFORMATION ABOUT CHEMICAL AMOUNTS.

PRINCIPLES

Answering the question 'how much' is central to both chemical analysis and chemical synthesis. The purpose of qualitative analysis is to answer question 'how much'? by determining the quantities of chemicals in a sample. In advanced chemistry by main method of quantitative analysis is a transition. Titrations provide a precise way to determine the concentration of solution and to investigate the quantities of chemical involved in reactions.

Chemicals also have to answer the question 'how much?' to decide on the quantities of each reactant mixture and to predict the expected yield of product from a chemical synthesis.

CHEMICAL AMOUNTS

When answering the question 'how much?', chemists need to measure amounts of chemical which equal numbers of atoms, molecules or ions. The unit of chemical is the mole. One mole is the amount of substances that contains as many specified atoms, molecules or ions as are atoms in exactly 12 g of carbon-12.

The key to working with chemical amounts in moles is to know the relative masses of atoms on the carbon-12 scale.

The molar mass of an element is numerically equal to the relative mass of element. The relative mass of carbon is 12. The molar mass of an carbon atoms is ( 12 g ^mol).

The molar masses of an element or compound is found by adding up the molar masses of the elements in the given formula. The formula of sulfuric acid is H2SO4. Its molar mass;

= (2 *1 g ^ mol) + (1 * 32g ^ mol) + (4*16g ^ mol)

= 98g^mol.

NOTE: Every physical quantity in science has a name, a symbol and a unit. In the case of amount of substances the name of the unit is 'mole' the symbol is 'n' and the unit is 'mol'.

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IMPORTANT TIPS FOR CHEMISTRY PRACTICAL.

Evaluating evidence and procedures

When you evaluate your work you have to make judgments. You might start by making a short list of the criteria that you use to decide whether or not your practical work has been successful.

Your evaluation should always have two parts:

First you decide whether or not any results based on measurement are reliable and meaningful, or whether the outcomes of a preparation are adequate considering the methods used.

Second, you should review the practical techniques that you have used and decide whether they were the right ones to use; this should include comments on any results than seem anomalous.

Commenting on the reliability of data.

In a quantitative investigation your analysis should include an estimate of the overall uncertainty in your results.

Comment here on any anomalous results that do not seem to fit in with the rest of your measurement or observation. You should suggest an explanation for any anomalies that you have detected.

Comparing outcomes with expectations.

In some investigation you may be able to refer to published data in reference books, or other sources, which allow you to compare your findings with the generally accepted results.

Published description of chemical preparations often quotes the likely yield. This allows you to compare your percentage yield with the outcomes that can be reasonably expected. Sometimes the expectations are predictions based on theory. If so, you should discuss this whether or not you judge that your findings are consistent with your predictions.

Identifying possible improvements.

You should consider whether or not the method you used could have been improved, either by making minor modifications or by using a completely different approach. Here you can also refer to methods that you could not carry out with the usual range of equipment available in advanced chemistry laboratories. You might refer to other option such as the use of instrumental methods of analysis including the various types of spectroscopy.

NOTE: Ask for some help if you are stuck. It is better to lose a mark or two for assistance rather than ending with nothing because all your work is misguided.

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IMPORTANT SKILLS FOR CHEMISTRY PRACTICAL

(1) IMPLEMENTING

As we know that chemistry is experiment subject and it always needs a technical skills to perform better experiment. Where implementation of the observations is much necessary.

WORKING UNAIDED IN A HEALTHY AND SAFE WAY

When it is the case of practically you should work cleanly and methodically paying proper attention to health and safety precautions. When learning new skills you may work as a part of group but you will be on your own when being assessed. Only carry out practical work in the presence of qualified supervisor.

DEMONSTRATING PRACTICAL SKILL

You will be judged by your skills results which will depend on the type of experiment you are conducting. Your teacher may make some judgments based on watching at your work in the laboratory. More significant are the outcomes of your work such as the yield and purity of products, your measurements of melting or boiling points, and detail and relevance of your observation and the accuracy of masses, volumes, temperatures and times.

Measurement, observation and recording of data

If your report you must record measurements with precision that matches the quality of the equipment that you have used. Masses should be quoted to the number of decimal places that much the accuracy of the balances you have used. Similarly, with grade B 50 cm burettes, you should always note reading to the nearest 0.05 cm^3.

Note: Never write observation and measurement on scraps of paper that are easy to lose. Include a record of all measurements in your account of the experiment as well as values calculated from the measurement.

(2)ANALYSING EVIDENCE AND DRAWING CONCLUSION.

This is the stage at which you work out the meaning of your observation and measurements. Here you take the raw data and present it in ways that shows you has found out as a result of your practical work.

FORMS OF COMMUNICATION

You should choose ways of analyzing and communicating your findings which are appropriate to you experiment. Consider including labeled diagrams, tables, charts and graphs as well as continuous prose.

You will gain credit for using the language of chemistry correctly. Compare what you write with what you find in textbook or on websites to check that you are working at the right level for an advanced course.

PROCESSING THE DATA

 You should process the data in quantitative investigations to answer the chemical questions: 'how fast?' 'How much?' and 'how far?' your analysis may involve calculations. If so you must show that you understand each step of calculation. Always check that the number of significant figures in your final answer is consistent with the precision of your measurements.

ANALYSIS OF MEASUREMENT UNCERTAINTY

In any quantitative investigation you will need to assess the measurement uncertainty correctly.

Note: Always show the units of physical quantities. Label the axes of graphs and give a scale with units. Set out all calculations in full, step by step giving all the detail of your working.

DRAWING CONCLUSIONS.

Here you have to relate your findings to your knowledge and understanding of chemical theory. You need to convince your teacher, or an examiner, that you understand the chemical nature of the observation or measurements you are analyzing.

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TECHNICAL SKILLS FOR CHEMISTRY PRACTICAL

We know that chemistry is an experiment subject. Theory does not make sense in the abstract but it does when it is seen as an attempt to explain observation in the laboratory and in the natural world. The skills of laboratory chemistry are great practical importance too. Chemistry is about making useful new chemicals (synthesis) and finding out what materials are made of (analysis).

Chemistry practical is all about the planning work. At first planning may seems very difficult it can be heard to know what is possible when you have limited experience of chemistry. You need to bear in mind that your teachers and the examiners know from the course specification what you have done at each stage of your work and what it is reasonable for you to suggest in plans. The crucial point is that when planning any practical activity you should expect to use techniques, chemicals, and equipment that you have used before.

When asked to make plan you will often given some information about the experiment situation to give you a start.you will be expected to apply what you have learned in the theory part of the course. You may also be expected to draw  on other sources of information including textbooks, references and websites. The emphasis is on making use of the knowledge and experience gained during your course so far.

WORKING ON YOUR OWN.

 You will practise planning with the help of your teacher but when it comes to assessment you must work independently to get top marks. Working independently does not mean working isolation so you should expect to consult sources of reference.

Remember that it can be your interest to ask for help from your teacher you are really stuck. If the help gets you started in the right direction, then you can gain credit for all the others aspects of planning.Overall, this may allow you to gain more marks. Getting the marks for independent working will often fail to compensate for coming up with a bad plan.

SHOWING THAT YOU HAVE RESEARCHED AND UNDERSTOOD THE SITUATION

you must make sure that you understand the chemical theory related to the experiment you are going to carry out. 

DESCRIBING THE PROCEDURE IN DETAIL

Aim to write plan for an experiment in a way that could be followed by someone else with similar to yourself. Model your written plan on the style of instruction and guidance in practical books or on worksheets from your teacher.

ATTENDING TO HEALTH AND SAFETY

You must carry out a risk assessment and show that you have consulted the relevant guidance on health and safety.Never make a plan based on apparatus of a kind that have never used before.

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IMPORTANCE OF COMMERECE

We know the fact that, our world is totally depends upon a commerce. Now commerce is one of the important parts of our livelihood. To establish a simple business also a person should possess the good knowledge about commerce.In a short period of time commerce gains its popularity in the society. Many commercials banks are established in a country for the welfare of society. These banks are originated from the commerce. If we once imagine our life without a commerce then,it is too difficult for us to survive as commerce is a part of our life.
At first the barter system was popular among human civilization. It was so difficult that people were unsatisfied with exchange.  So slowly humans got the idea and create the money. The term money is based on the commerce. Money is something that has the power to exchange something. Commerce and money are interrelated with each other. Both should be presented for the completion of  commercial tasks. These days commercial activities have serve many people to uplift the living standard.The commerce helped the people to establish many business house in the society. Commerce has many contribution in the developmental process. The world is now the part of commerce. People are so busy in their business that they forget their responsibilities. This is one of the demerits of commerce .But we do have many benefits from commerce. Because of commerce we can increase economic rate. Our economic condition can reach in high place because of commerce. Commercialization is necessary in every society, every country and everywhere for the sustainable development.
The world is now depends on commerce .We should possess the knowledge of commerce and use in right place. Using the knowledge of commerce in right field can helps to get many things in life. According to changing environment we should change the process and idea about commerce.

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SELF-STUDY VS GROUP STUDY

 If you are reading this, you probably know the term self-study and the group study. Whatever, the term is, don't matters. But the term is not a new for u all. Isn't it? Those activities done during the school life, may it be a group study for examination or be it a competitive method of self study to be success. It was familiar to us during the school life and till yet. Isn't it? You probably have followed it, don't you? I am also a student from those familiar activities during the schools life and till yet. So, I want to compare those activities, whether self study is better or group study.

Firstly, I want you to answer my question. Have you ever known how effective group study or self study is? If you wish which you would you choose. If answer is group study, then you are average student. Am I right? Let's have a glance at once; if the lesson is taught and you don't understand then, you with your friends will be sitting for the discussion. It makes easy to understand the lesson, as everyone has different opinion and the answer, so it helps to cope with the real problem into the easier task. As even our own hand doesn't have same finger then how could all have the same thinking. So, different students have different opinion and help to fraction the problem into smaller portion. It is the obvious advantages of the group study.

However, it does have the disadvantages too, there may be different type of student in the group, some may catch the things faster, some may be average and some may be slower. So, Every time asking about the same things will be obvious makes the slower student to fell guilty to ask time and again even h/she does not understand. So, and even when friends are called for group study, some may come late and some may come faster. There, if someone is missing then, the extra discussion will take the place. Let it be the discussion of the games or let it be of yesterday TV shows. Therefore, group study has infinity's advantages and disadvantages.

Self-study is mostly practice by the intellectual student. Am I right?  If the student is self studying then h/she have the sufficient peace environment to memories the things. H/she does not have the fellows to disturb him/her nor have to wait for the fellows nor will be the discussions of anything.  The student will be more concentrate about his/her work. So, it is the advantages of self study. However it does has the disadvantages, if h/she doesn't know the simple things also h/she does not have anyone to ask for. Due to small information h/she will be disabling to do their work.

Therefore, while studying you may choose any of the choices. But, whatever the best is, you should compare yourself. No one can judge you better than yourself.

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