quantitative chemistry 2.0

what is the definition of the law of the conservation of mass?

the total. ass of the reactants must equal the total mass of the products

how do u calculate the Mr of a compound?

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

what is the mr of CaCO3

40+12+(3×16)=100

what is the relation of the mr’s of the reactants and products in a blanched chemical equation?

the sum of the relative formula masses of the reactants equals the sum of the relative formula masses of the products.

calculate the percentage of hydrogen in H2O

H2O= (1×2)+16= 18

percentage of H2 = (1×2) / 18 ×100 = 11.1%

definition of mole

1 mol is the amount of substance that contains the same number of particles as there are atoms in 12.0 g of carbon-12.

symbol for the unit of mole

mol

describe how the mass of one mole of a substnace in grams relates to its relative formula mass

The mass of one mole of a substance is the relative mass of that substance expressed in grams

value of avogadro constant

6.022×10²3

equation triangle that links RFM, mass and moles

mass/RFM x moles

why is it common to use an excess of one of the reactants in a chemical reaction

A good way to ensure that one reactant fully reacts is to use an excess of the other reactant. This is financially efficient when one of the reactants is very cheap.

When one reactant is in excess, there will always be some left over. The other reactant becomes a limiting factor and controls how much of each product is produced.

While using excess reactants can help to increase percentage yields, this is at the expense of atom economy.

A balance between the economic and environmental value of the use of excess reactants must be established.

what is meant by limiting reactant

the reactant that is all used up is called the limiting reactant.

explain how limiting the quantity of a reactant affects the amount of product it is possible to obtain

So, the greater the amount of moles (or mass of grams) in the limiting reactant, the greater the amount of moles (or mass of grams) in the products.

what mass of calcium hydroxide is formed when 10.0g of calcium oxide reacts with 10.0g of water. CaO+H2O → Ca(OH)2

CaO= 10 (mass) / 56 (RFM)= 0.17

H2O= 10/18=0.5

therefore CaO is limiting reactant

Ca(OH)2 = 0.17 x (40+32+2) = 13.2g

concentration calc

conc= mass of dissolved product / volume of solution

if 1.0g of solid sodium hydroxide is dissolved in 250cm² of solution what is the conc in g/dm³

250 / 1000=0.25 dm³

conc= 1/0.25 =4 g/dm³

calculate the mass of acetic acid in 100cm³ of vinegar with a conc of 0.05g/cm³

100×0.05=5g

explain how the mass of a solute and the volume of a solution is related to the concentration of the solution

concentration can be increased by dissolving more solute in a given volume of solution - this increases the mass of the solute.

calculate conc in mol/dm3

conc= mol/vol of sol

if 1.0g of solid sodium hydroxide are dissolved in 250cm³ of solution what is the conc in mol/dm3?

convert mass into moles: 1 (mass)/ 40 (Mr) = 0.025mol

calculate conc:

250/1000=0.25 dm³

0.025/0.25=0.1 mol/dm³

25.0 cm³ of hydrochloric acid, HCl, of concentration 1.0 mol/dm³ reacts with 20.0 cm³ of sodium hydroxide, NaOH, solution. Calculate the concentration of the NaOH solution. The equation for the reaction is HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

Converting volumes from cm³ to dm³:

• volume of HCl = 25.0 cm³ = 25.0 ÷ 1000 = 0.025 dm³

• volume of NaOH = 20.0 cm³ = 20.0 ÷ 1000 = 0.020 dm³

Substituting into the equation to find the amount of HCl in the given volume:

Amount of HCl in mol = concentration in mol/dm³ × volume in dm³

= 1.0 mol/dm³ × 0.025 dm³

= 0.025 mol

The equation shows that 1 mol of HCl reacts with 1 mol of NaOH. So the amount of NaOH in 20.0 cm³ is 0.025 mol.

Substituting into the equation to find the concentration of NaOH:

conc of NaOH/dm³= amount of solutes (mol)/volume (dm³)

0.025mol/0.020dm³ = 1.25mol/dm³

explain how the concentration of a solution in mol/dm^3 is related to the mass of the solute and the volume of the solution

The higher the mass of the solute in comparison to the volume of the solution, the higher the concentration.

for gases what equation triangle volume, moles, and 24

volume of gas (dm³) / number of moles (mol) x 24

for gases what equation triangle links mass, number of moles and mr

mass/ number of moles x Mr

calculate the volume of hydrogen produced when 8.2g of sodium reacts completely with excess water. 2Na + 2H2O → 2NaOH + H2

moles of Na = mass / Mr = 8.2 / 23 = 0.3565mol

ratio to H2 = 2:1 so 0.3565×2=0.17826mol

volume H2 =0.17826×24=4.28dm³

how to work out moles of a solution?

moles of solution = vol (dm³) x conc (mol/dm³)

what is the use of multipliers in an equation?

multipliers help on adjusting values in equations, and they can be expressed in normal language or as part of mathematical formulas