Chemical Calculations Grade 11, 12 Questions and Answers

Chemical calculation questions uses many relationships of different parameters to solve or find unknown values. Questions are different from one to one. In school level, chemical equations, gas equations, moles, mass, concentration and more parameters are used.

Questions are prepared by following lessons and those lessons are combined to prepare these problems. Answers, explanations and necessary theories are provides for every questions.

  1. Chemical formula, molecular mass, amount (moles)
  2. Chemical equations, stoichiometry, balancing chemical equations
  3. Concentration, molarity, molality, ppm
  4. Ideal gas equations

Chemical calculation questions

Chemical calculations bases on moles, mass and molecular mass

Question 1

There is a pure NaOH bottle which contains NaOH as crystals. Some NaOH crystals are separated from the bottle and measured the mass using a balance. Then mass of separated NaOH was 2.2 g. How much NaOH (in moles) is separated? ( Na=23 , O=16 , H=1 )

Answer: 0.055 mol

Question 2

You ara said to separate 0.1 mol of potassium dichromate. What is the required mass of potassium dichromate? ( K=39 , Cr=52 , O=16 )

Answer: 29.4 g

Question 3

There is a white solid which contains calcium oxide as the main ingredient. Rest of others are impurities. It was required to calculate mass percentage of calcium oxide in this solid. So, as the first step. mass of solid was measured and it was 11.1 g. When mass percentage of calcium oxide was calculated by a chemical method, it was 75.68 %. So how much (mol) calcium oxide was there?

Answer: 0.15 mol

Calculations of decomposition of compounds

Question 1

A mixture of 1kg of CaO and MgO should be prepared in the laboratory. Moles ratio between CaO and MgO is two to one. Aqueous solutions of CaCl2, MgCl2 and solid Na2CO3 are given to prepare CaO and MgO mixture. Also laboratory instruments can be used in necessaries such as heating, mixing, filtering and more. Calculate required Na2CO3 mass and volume of each CaCl2 and MgCl2 aqueous solutions.

Following data may be useful to solve this question.

concentration of CaCl2 solution = 9.87 mol dm-3

concentration of MgCl2 solution = 9.77 mol dm-3

Relative atomic masses : O=16 , C=12, Mg=24 , Cl=35.5 , Ca=40

Calculations of calculating volume when acids and bases are diluted

Question 1

You need to prepare 250cm3 solution of 0.1 mol dm-3 NaOH. You are provided a concentrated 10.1 mol dm-3 NaOH solution. What is the required volume of concentrated NaOH to prepare that diluted NaOH solution?

Question 2

From 2 mol dm-3 HCl 250 cm3 solution, You have to prepare 0.1 mol dm-3 HCl 100 cm3 solution. How to you prepare this dilute solution from given concentrated solution.

Calculations of calculating mass of dry solids in preparing solids

Question 1

Nitric(iii) acid (nitrous acid / HNO2) is stable when nitrous acid solution is dilute. Nitrous acid is prepared as follow.

  • Solid sodium nitrate (NaNO3) is heated to give solid sodium nitrite (NaNO2) and oxygen (O2).
  • Solid sodium nitrite is dissolved in water to prepare aqueous sodium nitrite.
  • Add cold dilute HCl to aqueous sodium nitrite solution. It gives dilute nitrous acid.
What is the required mass of NaNO3 if you want to make 1dm-3 of 0.01 mol dm-3 nitrous acid?
see the chemical equations of nitrous acid preparing

Apply ideal gas equation

Question 1

There is a constant volume (831.4 dm3) reactor which holds two gases (A and B) at initial stage. When temperature is increased upto 2230C, it starts to react A and B and give C as the product. C is a gaseous compound. This reaction is an exothermic one. At 2230C, pressure inside the reactor is 200 * 105 Pa. After the reaction, it is founded that there are C and remaining A, B inside the reactor. Final pressure and temperature inside the reactor is 100 * 105 Pa and 4230C respectively. Find the produced amount (moles) of C.
A(g) + 3B(g) → 2C(g)

Find molecular formula of hydrocarbon and organic compounds

Question 1

4.2 g of hydrocarbon is burnt in excess oxygen gas stream and cooled to room temperature after the completion of the reaction. In the end of the reaction, it is found that amount of produced carbon dioxide gas is 0.08 mol. Find the molecular formula of the hydrocarbon.

Calculate required amounts using stoichiometry

Question 1

When excess ammonia reacts with chlorine gas, ammonium chloride and nitrogen gas are given as products. To produce 1 mol of nitrogen gas, how much amount of ammonia and chlorine gases are required?

Question 2

Calculate required amount of hydrogen peroxide (H2O2) moles to react with lead sulfide.

PbS + H2O2 → PbSO4 + H2O

Simple acid base calculations

Question 1

To neutralize 0.01 mol dm-3 NaOH 25 cm3 solution, you are going to use 0.04 mol dm-3 Ba(OH)2 solution. What is the required volume of Ba(OH)2 solution.

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