Concentration

5 ways to Calculate Concentration ALWAYS USE Significant Digits TO ROUND

1. Mass / Volume Percent = mass of solute (g) / Volume of solution (ml) * 100%
   1. You could get over 100%, used to inflate numbers, can be misleading / not meaningful
   2. Ex: A pharmacist adds 2.00 mL of distilled water to 4.00 g of a powdered drug making the final volume 3.00 mL. What is the percent (m/V) of the solution? (4.00g / 3.00 ml * 100% = 133.33%) this number has little to no meaning Unit has to be g and volume has to be mL
2. Mass / Mass Percent = mass of solute (g) / mass of solution (g) * 100%
   1. What mass of sodium fluoride is present in a 50 g sample of toothpaste if the toothpaste has a concentration of 0.76% (m/m) sodium fluoride? 0.76% = mass of sodium fluoride / 50 g toothpaste * 100% mass sodium fluoride = 0.76% * 50 / 100% = 0.38g
   2. More common, gives useful information that tells you because the units are the same it’s a similar comparison, more meaningful
3. Volume / volume Percent = volume of solute (mL) / volume of solution (mL) * 100%
   1. Ex: Rubbing alcohol is sold as a 70% solution of alcohol in water. What volume of alcohol is used to make 500 mL of rubbing alcohol? 70% = volume of alcohol / 500 mL * 100% volume of alcohol = 70% * 500 mL / 100% = 350 mL
   2. Units don’t have to be mL as long as they both are the same
   3. Question may arise how much water you want to add to that so (volume of solution) - (volume of solute)
4. part per million (ppm) / parts per billion (ppb)
   1. ppm = mass of solute (g) / mass of solution (g) * 10${}^6$
   2. ppb = mass of solute (g) / mass of solution (g) * 10${}^9$
   3. used for very small concentrations of substances (ie. NaF, I, or Cl added to drinking water)
   4. the calculations are similar to mass by mass percent
   5. eg: Mercury is dangerous at levels above 0.50 ppm in fish. What mass of mercury is considered dangerous in 2.0 kg of fish ppm = $\frac{massofsolute(g)}{massofsolution(g)}$ * 10${}^6$ 0.50 ppm = (mass of Hg * 10${}^6$) / 2000 g mass of Hg = (0.50ppm * 2000 g) / 10${}^6$ = 0.001g = 1 mg
5. Molarity (Molar Concentration)
   1. Molar Concentration (C) = moles of solute (mol) / volume of solution (L)
   2. C = n/V (C = concentration, V = Volume, M = $\frac{mol}{L}$, M = molar)
   3. Steps:
      1. Mass of solute -> moles of solute
      2. Moles of solute -> concentration of solution
   4. Always have to convert to Liters before doing this
   5. Ex: A solution containing 6.15 g NaCl is dissolved in 6.00 * 10${}^3$ mL of water. What is the concentration of solution in $\frac{mol}{L}$ n_N$$_a$$_C$$_l = $\frac{m}{M}$ = 6.15 g / 58.44 g / mol = 0.105236139 mol c = $\frac{n}{V}$ = 0.105236139 mol / 6.00 L = 1.7539356 * 10^-$$^2 mol / L = 1.75 * 10^-$$^2 mol/L

Grade 11 Chemistry Homework

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