Key Calculations quiz

1. 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

(81 + 79)/2 = 80

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

(81x79)/100 = 63.99

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

Question 1 of 17

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

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

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

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

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

Question 2 of 17

3. 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?

1170 J

1247 J

2.153 kJ

1944 kJ

Question 3 of 17

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

88g

176 g

24 g

44 g

Question 4 of 17

5. Name this piece of lab equipment

burette

measuring cylinder

gas syringe

pipette

Question 5 of 17

6. A sample of hydrogen chloride gas has a volume of 48 dm³. What amount of hydrogen chloride is this?

24 moles

48 moles

1 mole

2 moles

Question 6 of 17

7. Calculate the relative formula mass(Mr) of calcium carbonate (CaCO₃)

68

100

50

120

Question 7 of 17

8. What are the units for amount in Chemistry?

g per 100g of solvent

Grams

Moles

mol/dm³

Question 8 of 17

9. A beaker of 2 dm³ of ammonium nitrate solution contains 1 mol of ammonium nitrate. What is the concentration of the solution?

0.5 mol/dm³

0.0005 mol/dm³

0.5 dm³/mol

2 mol/dm³

Question 9 of 17

10. State the expression for calculating % yield.

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

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

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

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

Question 10 of 17

11. To determine the formula of a metal oxide by combustion, magnesium is heated in a crucible. Why is a lid used?

To keep the magnesium warm

To stop the escape of magnesium

To stop the escape of magnesium oxide smoke

To stop carbon dioxide escaping

Question 11 of 17

12. 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 12 of 17

13. What is the equation linking moles, Mᵣ and mass

moles = mass / Mᵣ

moles = mass x Mᵣ

Mᵣ = mass x moles

mass = moles / Mᵣ

Question 13 of 17

14. 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 14 of 17

15. What is the empirical formula of an alcohol with the analysis; 52.2% C, 13.0% H and 34.8% O?

C₂H₆O

C₂H₆O₂

CH₆O

C₂H₃O

Question 15 of 17

16. 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?

0.68g

68g

17g

0.17g

Question 16 of 17

17. What is meant by the term molecular formula?

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

A method of calculating the ratios of masses in an equation

A method of calculating the mass needed to make a certain yield in an equation

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

Question 17 of 17

Key Calculations quiz

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