Instruction

1

Task. Calculate the mass of aluminium sulfide if the reaction of sulfuric acid entered the 2.7 g of aluminium.

2

Recorded a short condition

This:

m(Al) =2, 7 g

H2SO4

Find:

m(Al2 (SO4) 3)-?

3

Before to solve problems in chemistry, a chemical equation. In the interaction of metals with dilute acid forming salt and released gaseous substance is hydrogen. We arrange the coefficients.

2Al + 3H2SO4 = Al2 (SO4) 3 + 3H2

When you always need to pay attention only to substances for which known and you need to find, options. All the rest are not taken into account. In this case it will be: Al and Al2 (SO4) 3

4

Find the relative molecular mass of these substances in the table of D. I. Mendeleev

Mr(Al) =27

Mr(Al2 (SO4) 3) =27•2(32•3+16•4•3) =342

Translate these values into molar mass (M) multiplied by 1 g/mol

M(Al) =27G/mol

M(Al2 (SO4) 3) =342g/mol

5

Recorded a basic formula, which connects the amount of substance (n), mass (m) and molar mass (M).

n=m/M

Carry out calculations according to the formula

n(Al) =2.7 g/27G/mol=0.1 mol

6

Make up two ratio. The first relation based on equation based on the odds faced by the formulas of the substances whose parameters are given or need to find.

First ratio: 2 mol Al you have 1 mole of Al2 (SO4) 3

The second ratio of 0.1 mol Al we have X mole Al2 (SO4) 3

(compiled on the basis of the obtained results)

Solve the proportion, given that X is the amount of substance

Al2 (SO4) 3 and has the unit mol

Here

n(Al2 (SO4) 3)=0.1 mol(Al)•1 mol(Al2 (SO4) 3):2моль Al=0.05 mol

7

Now there is the amount of substance and molar mass of Al2(SO4)3, consequently, you can find lots of which derive from the basic formula

m=nM

m(Al2 (SO4) 3)=0.05 mol•342g/mol=17,1 g

Recorded

Answer: m(Al2 (SO4) 3)=17,1 g

8

At first glance, it seems that to solve chemistry problems is very difficult, but it is not. And to verify the degree of assimilation, first try to solve the same problem, but only yourself. Then substitute other values using the same equation. And the last step is the solution of the new equation. And if you were able to handle what – you're to be congratulated!

Useful advice

Wonderful helper during solving tasks is a manual, time-tested "problems in chemistry for entering Universities" G. P. Khomchenko. And don't be afraid to use it – it proposes the solution of problems from the very beginning!

# Advice 2 : How to learn to solve chemistry problems

The curriculum is quite intense, absorbed theoretical knowledge, but practical skills there is no solution. What to do and how to learn to solve problems in chemistry? What is primarily required from the student?

Solution of tasks on chemistry is specific, and you need to find a starting point that will help to learn to understand this difficult matter.

To correctly solve chemistry problems, you first need to know what is the valence of the elements. Depends on the formulation of the substance, equation of a chemical reaction without taking into account the valence not be, and not to equalize. The periodic table is used in almost every job, you need to learn how to use it correctly to obtain the necessary information about the chemical elements, their mass, the electronic levels. Often tasks require us to calculate the mass or volume of the resulting product, this is the basis.

And then the other, more complicated tasks will be solved easier. But first of all, formulas of substances, well written reaction equations, showing that in the end will succeed and in what form. It could be fluid, freely evolved gas, solid, drop down into the sediment or dissolved in water or any other liquid.

To solve the problem briefly recorded her condition. After this is a balanced equation for the reaction. For example, consider a specific data need to determine the mass of the received substance, sulphide of aluminium, the reaction of aluminum metal with sulfuric acid, if taken aluminum is 2.7 grams. We should pay attention only to substances that are known, then those that want to find.

To start you need to solve with the translation of the mass in grams per mole. To make the reaction formula, substitute into it the values of mass and calculate the ratio. After solved a simple problem, you can try to learn on their own similar, but with other elements, that is, to get hand. The formulas are the same, only the elements change. All the solution of tasks on chemistry is reduced to writing the correct formula of the substance, to the proper preparation of the reaction equations.

For exercise, you can use the Internet, there's a huge number of different jobs, and then you can see the solution algorithm, which continue to apply independently. The advantage is that you can always see the correct answer, and if your result does not coincide, to understand, to find the error. More for learning to use reference books and collections of problems.

## What you need to know for solving problems in chemistry

To correctly solve chemistry problems, you first need to know what is the valence of the elements. Depends on the formulation of the substance, equation of a chemical reaction without taking into account the valence not be, and not to equalize. The periodic table is used in almost every job, you need to learn how to use it correctly to obtain the necessary information about the chemical elements, their mass, the electronic levels. Often tasks require us to calculate the mass or volume of the resulting product, this is the basis.

If the valence to determine incorrectly that all the calculations are incorrect.

And then the other, more complicated tasks will be solved easier. But first of all, formulas of substances, well written reaction equations, showing that in the end will succeed and in what form. It could be fluid, freely evolved gas, solid, drop down into the sediment or dissolved in water or any other liquid.

## Where to start when solving problems in chemistry

To solve the problem briefly recorded her condition. After this is a balanced equation for the reaction. For example, consider a specific data need to determine the mass of the received substance, sulphide of aluminium, the reaction of aluminum metal with sulfuric acid, if taken aluminum is 2.7 grams. We should pay attention only to substances that are known, then those that want to find.

To start you need to solve with the translation of the mass in grams per mole. To make the reaction formula, substitute into it the values of mass and calculate the ratio. After solved a simple problem, you can try to learn on their own similar, but with other elements, that is, to get hand. The formulas are the same, only the elements change. All the solution of tasks on chemistry is reduced to writing the correct formula of the substance, to the proper preparation of the reaction equations.

All the problems are solved on the same principle, the main thing is to place coefficients in the equation.

For exercise, you can use the Internet, there's a huge number of different jobs, and then you can see the solution algorithm, which continue to apply independently. The advantage is that you can always see the correct answer, and if your result does not coincide, to understand, to find the error. More for learning to use reference books and collections of problems.