Moles

what is the conservation of mass? What does this mean?

During a chemical reaction, no atoms are destroyed or created. It means that the mass of the products are equal to the mass of the reactants.

what might have happened if there is a change of mass of unsealed vessel during a reaction?

1: If the mass increases, it is probably because one of the reactants is a gas found in the air. Before the reaction, the gas is floating round in the air bit it is not contained in the reaction vessel. When the gas reacts to form part of the product, it becomes contained inside the reaction vessel so the total mass of the stuff inside the reaction vessel increases.

2.If the mass decreases it means that a gas was the product. Before the reaction, all reactants are inside the reaction vessel. If the vessel isn't properly sealed, the gas formed as the product can escape the vessel.

What is the relative formula mass of a compound?

The sum of the relative atomic masses of the atoms in the numbers shown in the formula

how do you calculate percentage mass?

percentage mass= Atomic mass x number of atoms of that element/Mr of the compound x 1 00

What is 1 mole of a substance?

the amount of that substance that contains an Avogadro number of particles - 6.02 x 10^23 particles

what is 1 mole equal to in mass?

one mole of atoms or molecules of any substance will have amass in grams equal to the relative formula mass of that substance.

what is the formula for moles?

Moles = mass/Mr

What is the empirical formula?

The simplest whole number ratio of atoms of each element in a compound

how do you calculate the empirical formula of a compound?

1: Find the moles of each element in that compound

2: divide those numbers of moles by the smallest number moles

3:You will get whole numbers and therefore u can created a ratio of the atoms

4: use that ratio to add the number of each elements in the compound

e.g: We have 5.5 grams of manganese and 3.2 g of oxygen. What is the empirical formula of the manganese oxide formed?

A:

1)mol of Mn= 5.5 divided by 55= 0.1 mol

mol of 0= 3.2 divided by 16=0.2 mol

2)0.1 divided by 0.1 = 1

0.2 divided by 0.1= 2

3) ratio is = 1:2

4) formula = Mn02

What is a limiting reactant?

the reactant that runs out first in a reaction and therefore limits the amount of products being formed.

When will equal numbers of moles of any gas occupy the same volume?

when they are at the same temp and pressure

what is the formula for the volume of a gas?

Mass of gas / Mr of gas x 24

what is concentration?

the amount of a substance in a given volume

what are the 2 formula for concentration?

number of moles of solute/volume of solvent

mass of solute/volume of solvent

What is atom economy?

A measure of the amount of starting materials that end up as useful products

what is the formula for atom economy?

% atom economy = Mr of desired product / total Mr of reactants x 100

What does 100% atom economy mean?

All the atoms in the reactants have been turned into useful (desired) products - the higher the atom economy, the 'greener' the process

Why is a high atom economy good? What are the problems with low atom economy?

Better for profits and environment

1) low atom economy means more waste

2) low atom economy reactions use up resources very quickly. All the waste materials also have to be disposed of making these reactions unsustainable

3) expensive as raw materials are expensive to buy and waste is expensive to get rid off

What is percentage yield?

the ratio of the actual yield to the theoretical yield, multiplied by 100

what is the formula for percentage yield?

percentage yield = mass of product actually made / maximum theoretical mass of product x 100

why are yields always below 100 percent?

1) in reversible reactions, products can turn back into reactants

2) the reactants sometimes might react differently. They might react with gases in the air or impurities in the reaction mixture. They end up forming extra products.

3) when you filter a liquid to remove solid particles, you always lose a little bit of liquid or a bit of solid.