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iGCSE Chemistry: Key Calculations (Triple)
Terms in this set (21)
(Triple only) 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 200g water?
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
Calculate the relative formula mass(Mr) of carbon dioxide (CO₂)
What are the units for amount in Chemistry?
What is the equation linking moles, Mᵣ and mass
moles = mass / Mᵣ
What mass of carbon dioxide is produced when 24g of carbon undergoes completely combustion?
State the expression for calculating % yield.
% yield = (actual amount of products/theoretical amount of products) x 100
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 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
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) State the expression for calculating molar concentration
Molar concentration = Amount (in moles)/volume (in dm³)
(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 (24 dm³ or 24,000 cm³)
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 a constant mass has been reached and there is no more magnesium left to react
(Triple only) Describe how to carry out an acid-alkali titration
1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator changes colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until two concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.
(Triple only) Draw a burette
(Triple only) Draw a pipette
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?
State the units of molar enthalpy change.
(Triple only) In a chemical reaction, the overall molar enthalpy is -87 kJ/mol. Is this reaction exothermic or endothermic?
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