Key Calculations quiz

1. What volume does 0.5 moles of ethene gas occupy (at rtp)

48 cm³

48 dm³

12 dm³

12 cm³

Question 1 of 17

2. State the expression for calculating % yield.

% yield = (actual amount of products/theoretical amount of products)

% yield = (theroretical amount of products/actual amount of products)

% yield = (theroretical amount of products/actual amount of products) x 100

% yield = (actual amount of products/theoretical amount of products) x 100

Question 2 of 17

3. Calculate the relative formula mass(Mr) of cobalt chloride crystals (CoCl₂.6H₂O)

169

238

158

130

Question 3 of 17

4. In a combustion calorimetry experiment, 0.78g of ethanol (C₂H₅OH) produced 12,540 J of heat energy. Calculate the molar enthalpy change.

-425 kJ/mol (Amount = 23/0.78 = 29.5 mol. Answer = 12540/29.5 = 425 kJ/mol)

-738 kJ/mol (Amount = 0.78/46 = 0.017 mol. Answer = 12540/1000/0.017 = 738 kJ/mol)

-369 kJ/mol (Amount = 0.78/23 = 0.034 mol. Answer = 12540/1000/0.034 = 369 kJ/mol)

-213 kJ/mol (Amount = 46/0.78 = 59.0 mol. Answer = 12540/59.0 = 213 kJ/mol)

Question 4 of 17

5. Complete the following expression: amount (in moles) =

Aᵣ / Mᵣ

amount (in moles) x Mᵣ

Mᵣ / mass

mass / Mᵣ

Question 5 of 17

6. Use Q=mcΔT and c=4.18J/°C/g. A strip of magnesium is added to a beaker with 200cm³ of copper (II) sulfate. The temperature starts at 21.7°C and rises to a maximum of 23.1°C. What is the total heat energy change?

1944 kJ

1170 J

2.153 kJ

1247 J

Question 6 of 17

7. An oxide of nitrogen contains 26% nitrogen and 74% oxygen and has a relative molecular mass of 108. Find the empirical and molecular formulae for the oxide.

Empirical formula is N₂O₅. Molecular formula is also N₂O₅

Empirical formula is N₄O₁₀. Molecular formula is N₂O₅

Empirical formula is N₂O₅. Molecular formula is N₄O₁₀

Empirical formula is NO₂.₅ Molecular formula is N₂O₅

Question 7 of 17

8. To determine the formula of a metal oxide by combustion, magnesium is heated in a crucible. Why is the crucible is cooled, weighed, reheated, cooled, re-weighed, and so on?

To make sure the mass is still going down so the magnesium is still reacting

To ensure all the magnesium oxide to escape

To allow any water to escape

To make sure a constant mass has been reached and there is no more magnesium left to react

Question 8 of 17

9. In a chemical reaction, 250 kJ/mol is taken to break all the bonds and 280 kJ/mol is released when new bonds are formed. What is the overall molar enthalpy of the reaction?

+30 kJ/mol

+530 kJ/mol

-530 kJ/mol

-30 kJ/mol

Question 9 of 17

10. A graph shows the solubility of sodium chloride in water at 50°C is 34g/100g. At that temperature, what mass of sodium chloride will dissolve in 50g water?

68g

0.68g

0.17g

17g

Question 10 of 17

11. A sample of bromine contained the two isotopes in the following proportions: bromine-79 = 50.7% and bromine-81 = 49.3%. Calculate the relative atomic mass of bromine

((81x50.7)+(79x49.3))/100 = 80.01

((79x50.7)+(81x49.3))/100 = 79.99

(81x79)/100 = 63.99

(81 + 79)/2 = 80

Question 11 of 17

12. What is the meaning of the word mole in Chemistry?

Moles are the units for amount of substance. 1 mole of an element is its atomic number in grams (e.g. 1 mole of magnesium is 12 g)

Moles are the units for amount of substance. 1 mole of a substance is its relative formula mass in grams (e.g. 1 mole of magnesium is 24 g)

Moles are the units for amount of substance. (1 mole is 10 g of a substance)

A mole is a small burrowing mammal

Question 12 of 17

13. What is meant by the term empirical formula?

A chemical formula that shows the simplest ratio of the numbers of atoms in a compound

A method of calculating the ratios of masses in an equation

Baby food for emperors

A chemical formula that shows the actual numbers of the different types of atoms in a molecule

Question 13 of 17

14. Name this piece of lab equipment

gas syringe

measuring cylinder

burette

pipette

Question 14 of 17

15. A beaker of 1.5 mol/dm³ calcium chloride solution contains 0.3 mol of calcium chloride. What is the volume of the solution?

4.5 dm³

0.2 dm³

0.002 dm³

0.45 dm³

Question 15 of 17

16. What is the empirical formula of a compound in which 0.48 g of carbon combines with 0.08 g of hydrogen and 0.64 g of oxygen?

CH₂O

CH₄O

C₄H₂O

C₂H₄O₂

Question 16 of 17

17. What mass of carbon dioxide is produced when 24g of carbon undergoes completely combustion?

88g

176 g

24 g

44 g

Question 17 of 17

Key Calculations quiz

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