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Solutions

Solutions. A solution is formed when a substance is dissolved in a liquid. The concentration of the solution may be expressed as grams per Litre g L -1 as a percentage % (g per 100mL) Moles per litre mol L -1 You need to be able to convert from one to another. Concentration by mass.

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Solutions

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  1. Solutions A solution is formed when a substance is dissolved in a liquid. The concentration of the solution may be expressed as • grams per Litre g L-1 • as a percentage % (g per 100mL) • Moles per litre mol L-1 You need to be able to convert from one to another

  2. Concentration by mass Concentration by mass is represented by grams per litre (g L-1) it is calculated by dividing the mass of the solute by the volume of the solute

  3. If I make up Raro using 100g of powder in 500mL of water, what is the concentration m = 100g V = 0.5L c = ? c = m/V = 100g/0.5L = 200gL-1

  4. Percentage solutions A percentage solution states how many grams of solute is in 100mL of solution. They may be measured as • weight/weight (w/w) g per 100grams • weight/volume (w/v) g per 100mL • volume/volume (v/v) mL per 100mL

  5. What mass of NaCl is required to make up 50ml of a 2% solution? A 2% solution has 2g/100ml or 20gL-1 c = 20g L-1 V = 50mL or 0.05L m = ? m = cV = 20 x 0.05 = 1g is required in 50ml to make a 2% solution

  6. Concentration in moles per litre • Chemists usually need to know the amount in mols of a substance that is in a solution. This is measured in mol L-1 • A 1mol L-1 solution of CuSO4 contains 1 mol of CuSO4 per litre

  7. Converting • Sometimes concentrations are given in g 100mL-1 To convert to g L-1 multiply by 10 • to convert from kg to g multiply by 1000 or 103 • To convert from mL to L divide by 1000 or multiply by 1/1000

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