Finding Concentrations



Finding Concentrations

Chose the correct formula

%C C ppm

Percent concentrations and ppm:

1. Solve the following concentration questions

a. 1.6 g of NaCl in 400 g water

b. 10 ml NaOH in a 350 ml solution

c. 10 ml NaOH added to 350 ml of water

d. 0.6 mol of CaCO3 in a 450 ml solution

e. 15 mg of Cu+ ions in 3.5 L of water (ppm)

Homework: (show the equation, the work, and the answer for full marks)

1. Find the concentration in %W/W of 2.5g of sugar in 28g of Fruit Loops

2. Find the concentration in %W/W of 1.5g of Carbon dioxide in 355ml of coca cola.

3. Find the concentration in %V/V of 12.0mL of HCl added to 250mL of water

4. Find the concentration of Na+ ions in ppm if there are 0.22g in 750mL of water

Molar Masses:

In chemistry amounts are not as useful when given in grams or kilograms. When we want to compare how much methane(fart) will react with air (burn), then we use the number of moles, which is the chemical amount.

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We can see above that for every 1 mole of CH4 (fart) we need 2 moles of Oxygen. It’s a one to two ratio. It wouldn’t be 1 gram of methane (fart) needs 2 grams of oxygen to fully react.

Often we need to convert grams into moles though. To do this we need to use the molar mass. Molar masses are given on the data sheet for individual atoms and can be added together for more complex compounds.

Find the molar mass of:

a. Silver:

b. Oxygen:

c. Methane (CH4):

d. Salt (NaCl):

e. AgNO3:

Homework: Find the molar masses for each of the following and put units (g/mol)

|CO2 |Water |Methanol (CH3OH) |

| | | |

|CuSO4 |NaNO3 |ZnCl |

| | | |

|C3H8 (propane) |MgCl2 |Carbon Monoxide |

| | | |

Finding Molar concentration and masses

Molar concentration can be in M = mol/L

2. Solve for the unknown using molar concentrations and molar mass.

a. 3.2 g of NH4Cl in 475 mL of solution (Conc = ?)

b. 2.6 L of a 0.115 M solution of CuCl2 (mass of CuCl2)

c. 3.4 g of NH4NO3 is added to how much water to make a 0.2 mol/L solution?

Creating a solution

3. Use calculations to show how you can make a solution of the following

a. To make a 0.25 mol/L solution of CuSO4

b. To make a solution of KNO3 with a concentration of 0.1 M

c. To make a solution of [Na2CO3] = 0.15 M

Check your answers with the key at the front and then build these 3 solutions. You must show your finished solutions for marks.

Diluting a solution

4. For an experiment you require a 100 mL of a 0.1 mol/L solution of HCl(aq). Use the given concentration of HCl(aq) to solve for what initial amount of HCl is required.

Solve and check you answer at the front before creating your solution of [HCl] = 0.1 M. You must show you finished solution for marks.

You MUST follow all safety procedures for dealing with chemicals including acids and bases (glasses, gloves, etc). Failure to do so will result in a grade of:

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If doing % volume ** be careful to add volume and weights if necessary**

Ex. Percent Concentration by Volume = V(solute)/V(solution) x 100%

Volume of solution can be the sum of the volume of solute and the solvent!!!

**Similar for % Concentration by mass

(mass(solution) = m(solute) + m(solvent))**

X = -(A + B)(A – B) + (A – B)2

Where A = 5 and B = 2

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