56 terms

iGCSE Chemistry: GCSE Calculations - test myself

STUDY
PLAY

Terms in this set (...)

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
((79x50.7)+(81x49.3))/100 = 79.99
A sample of carbon contained 98.90% carbon-12 and 1.10% carbon-13. Calculate the relative atomic mass of carbon
((12x98.90)+(13x1.10))/100 = 12.01
Calculate the relative formula mass(Mr) of a molecule of bromine (Br₂)
160
Calculate the relative formula mass(Mr) of aluminium nitrate (Al(NO₃)₃)
213
Calculate the relative formula mass(Mr) of aluminium oxide (Al₂O₃)
102
Calculate the relative formula mass(Mr) of ammonium nitrate (NH₄NO₃)
80
Calculate the relative formula mass(Mr) of calcium carbonate (CaCO₃)
100
Calculate the relative formula mass(Mr) of calcium hydroxide (Ca(OH)₂)
74
Calculate the relative formula mass(Mr) of carbon dioxide (CO₂)
44
Calculate the relative formula mass(Mr) of cobalt chloride crystals (CoCl₂.6H₂O)
238
Calculate the relative formula mass(Mr) of ethanol (C₂H₅OH)
46
Calculate the relative formula mass(Mr) of hydrated copper (II) sulfate (CuSO₄.5H₂O)
249.5
Calculate the relative formula mass(Mr) of propane (C₃H₈)
44
Calculate the relative formula mass(Mr) of zinc phosphide (Zn₃P₂)
257
What are the units for amount in Chemistry?
Moles
What is the meaning of the word mole in Chemistry?
A mole is the amount of a substance found in its relative formula mass in grams (e.g. in 24g of Magnesium)
Using relative atomic mass (Aᵣ) and relative formula mass (Mᵣ), complete the following expression: amount (in moles) =
mass / Mr
Using relative atomic mass (Aᵣ) and relative formula mass (Mᵣ), complete the following expression: mass =
amount (in moles) x Mr
Using relative atomic mass (Aᵣ) and relative formula mass (Mᵣ), complete the following expression: Mᵣ =
mass / amount (in moles)
What mass of calcium bromide will fully react with 71g of chlorine?
200g
What mass of carbon dioxide is produced when 24g of carbon undergoes completely combustion?
88g
In the thermal decomposition of calcium carbonate, we might expect 50g of calcium carbonate to produce 28g of calcium oxide. If instead only 24g of calcium oxide is produced, what is the yield?
86%
State the expression for calculating % yield.
% yield = (actual amount of products/theoretical amount of products) x100
1.170 g of CoCl₂.xH₂O gave a residue of 0.641 g on heating. Find x.
6
7.485 g of a hydrated copper(II) sulphate CuSO₄.xH₂O was heated producing 4.785g of anhydrous copper(II) sulphate. What is the formula of the hydrated salt?
CuSO₄.5H₂O
State the steps for calculating empirical formula
1) mass/Ar. 2) divide by the smallest. 3) Give the ratio has a whole number. 4) State final empirial formula
What is the empirical formula of an alcohol with the analysis; 52.2% C, 13.0% H and 34.8% O?
C₂H₆O
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
Work out the empirical formula of an oxide of chlorine contains 7.1 g of chlorine and 1.6 g of oxygen.
Cl₂O
What is meant by the term empirical formula?
A chemical formula that shows the simplest ratio of the numbers of atoms in a compound
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 compound that contained 24.24% Carbon. 4.04% Hydrogen and 71.72% Chlorine and has a relative molecular mass of 99. Calculate the empirical formula and the molecular formula.
Empirical formula is CH₂Cl. Molecular formula is also C₂H₄Cl₂
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
(Triple only) 0.5 dm³ of copper sulfate solution has a concentration of 0.1 mol/dm³. What amount of copper sulfate does it contain?
0.05 mol
(Triple only) 200 cm³ of potassium sulfate solution has a concentration of 2 mol/dm³. What amount of potassium sulfate does it contain?
0.4 mol
(Triple only) 25 cm³ of sodium chloride solution has a concentration of 0.5 mol/dm³. What amount of sodium chloride does it contain?
0.0125 mol
(Triple only) A beaker of 1.5 mol/dm³ calcium chloride solution contains 0.3 mol of calcium chloride. What is the volume of the solution?
0.2 dm³
(Triple only) 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
(Triple only) State the expression for calculating molar concentration
Molar concentration = Amount (in moles)/volume (in dm^³)
(Triple only) A sample of hydrogen chloride gas has a volume of 48 dm³. What amount of hydrogen chloride is this?
2 moles
(Triple only) State the expression for calculating molar volume of a gas.
Molar volume = amount (in moles) x 24 dm³ or 24,000 cm³
(Triple only) What is the meaning of the term Molar Volume?
The volume of 1 mole of gas at r.t.p is called the molar volume (24dm³ or 24000cm³)
(Triple only) What volume does 0.5 moles of ethene gas occupy (at rtp)
12 dm³
(Triple only) What volume does 3 moles of carbon dioxide gas occupy (at rtp)?
72 dm³
To determine the formula of a metal oxide by combustion, magnesium is heated in a crucible. Why is a lid lifted from time to time?
To allow oxygen in so the magnesium fully reacts
To determine the formula of a metal oxide by combustion, magnesium is heated in a crucible. Why is a lid used?
To stop the escape of magnesium oxide smoke
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-weighted, and so on?
By repeating till 2 consecutive masses are recorded, we know that the magnesium has all reacted
Use Q=mcΔT and c=4.18J/°C/g. 25cm³ of sulfuric acid is put into a boiling tube. The starting temperature is 21°C. A spatula of iron filings is added. After a while the temperature reaches 33°C. What is the total heat energy change?
1254 J
Use Q=mcΔT and c=4.18J/°C/g. A spatula of sodium fluoride is put into a boiling tube with 25cm³ of water. The temperature drops from 22.0°C to 18.6°C. What is the total heat energy change?
-355 J
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
In a combustion calorimetry experiment, 0.78g of ethanol (C₂H₅OH) produced 12,540 J of heat energy. Calculate the molar enthalpy change.
738 kJ/mol
State the units of molar enthalpy change.
kJ/mol
(Triple only) Assuming bond energies in kJ/mol: H-C 412, C-C 348, O-H 463, C-O 360, C=C 612. Calculate the molar enthalpy change for the reaction: ethanol → ethene + water
+45 kJ/mol
(Triple only) 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
(Triple only) In a chemical reaction, the overall molar enthalpy is +87 kJ/mol. Is this reaction exothermic or endothermic?
Endothermic
(Triple only) In a chemical reaction, the overall molar enthalpy is -87 kJ/mol. Is this reaction exothermic or endothermic?
Exothermic