C3 Quantitative chemistry Flashcards
What is the law of conservation of mass ?
The law of conservation of mass states that no atoms are created or destroyed during a chemical reaction so the mass of the products equals the mass of the reactants.
What is the relative formula mass of a compound ?
The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.
How can a chemical reaction result in an increase in mass ?
For example: when a metal reacts with oxygen the mass of the oxide produced is greater than the mass of the metal
Why can some reactions involve a loss in mass ?
If a reactant or product is a gas. For example in the thermal decompositions of metal carbonates, carbon dioxide is produced and escapes into the surroundings leaving the metal oxide as the only solid product.
In the reaction Zn + 2HCl—–> ZnCl2 + H2 explain what happens to the overall mass in the reaction if it happens in an unsealed container.
The mass decreases as hydrogen is a gas and escapes into the surroundings.
What is the symbol for moles ?
mol
What are chemical amounts measured in ?
moles
What is the mass of 1 mole of a substance if it is an element in grams ?
The mass of one mole of an element in grams is equal to its relative atomic mass (Ar).
What is the mass of 1 mole of a substance if it is a compound in grams ?
The mass of one mole of a compound in grams is equal to its relative formula mass (Mr).
What is the avagadro constant ?
The number of atoms, molecules or ions in one mole of a given substance
What is the value of Avagadro’s constant ?
The value of the Avogadro constant is 6.02 x 10^23 per mole.
How do you calculate the number of moles of an element/compound?
moles = m/Mr
m = mass of substance
| Mr = molar mass
How do you calculate the number of atoms in a given substance?
Number of atoms = Avogradro constant x the amount of substance in moles
What is the mass of 1 mole of oxygen gas
32 grams
What is the mass of 1 mole of oxygen atoms?
16 grams
What is the mass of 1 mole of carbon dioxide.
What is the mass of 0.25 moles of carbon dioxide?
44 grams
11 grams
How many moles of carbon dioxide are there in 88 grams of carbon dioxide.
2 moles
How many moles are in 10 grams of calcium carbonate
0.1 moles
Write an equation for the thermal decomposition of Zinc carbonate.
ZnC03———-> ZnO + CO2
When 3.1 grams of zinc carbonate undergoes thermal decomposition calculate the mass of ZnO produced.
- mass of ZnCO3 = 3.1grams
- moles of ZnCo3 = 3.1/125 grams = 0.0248moles
- 1 mole ZnO is 81g (molar mass) therefore 0.0248 moles = 2.0088 grams
- 2.0088 grams = 2.01g (2d.p)
In a reaction between magnesium and HCl, Anya wanted to find out how changing the amount of magnesium affected the rate of the reaction. Explain why the HCL needs to be in excess in this reaction and why the magnesium is called the limiting factor.
To make sure that HCL is not changing the reaction, the HCL needs to be in excess. This makes sure that the reaction does not stop because the HCL is finished. It is only the amount of magnesium that is limiting the reaction.
Calculate the mass of sodium chloride needed to make 0.5 litres of a 2 molar solution of sodium hydroxide?
moles = 0.5 x2 =1 mole
1 mole = to 58.5grams
Calculate the mass of calcium needed to make 25 cm3 of a 2 molar solution
moles = 2 x 0.025 = 0.05 mole
1 mole = 100grams 0.05 = 5 grams
Write down 3 ways that might cause all the reactants not to turn into products.
the reaction may not go to completion because it is reversible
• some of the product may be lost when it is separated from the reaction mixture
• some of the reactants may react in ways different to the expected reaction.
What is the percentage yield?
The amount of a product obtained is known as the yield. When compared with the maximum theoretical amount as a percentage, it is called the percentage yield.
What is atom economy ?
It is a measure of the amount of starting materials that end up as useful products.
Why is it important to have a high atom economy
It is important for sustainable development and for economic reasons to use reactions with high atom economy.
How is the percentage atom economy of a reaction measured
The percentage atom economy of a reaction is calculated using the balanced equation for the reaction as follows:
Mass of useful product/mass of all the reactants X 100
When do equal amounts of gases in moles occupy the same volume ?
Equal amounts in moles of gases occupy the same volume under the same conditions of temperature and pressure.
What volume does 1 mole of gas occupy att r.t.p
The volume of one mole of any gas at room temperature and pressure (20oC and 1 atmosphere pressure) is 24 dm3.
Calculate the volume of gas produced when 12 grams of Magnesium metal reacts with excess HCL
12 dm3
Calculate volume of gas produced when 2 grams of CaCO3 reacts with excess HCL
1.2 grams
Calclate mass of CaCO3 needed to react with excess HCL to produce 6dm3 of gas ?
this is a 1/4 of a mole of gas from the equation we need a 1/4 of a mole of CaCo3 1/4 x 100 = 25grams
