PHAY002; Stoichiometry

• What does n(Cl) represent?


  Amount of chlorine atoms
• What does n(Cl2) represent?


  Amount of chlorine molecules
• Why do we use the term entities instead of molecules?


  Because it includes ionic substances and atoms
• What does one mole of a substance contain?


  As many elementary entities as there are atoms in 0.012 kg of carbon-12
• What is Avogadro's number?


  $6.022 \times 10^{23}$
• What must be specified when using the mole?

  The elementary entities involved
• How many molecules are in 1 mol of aspirin?


  About $6.022 \times 10^{23}$ C9H8O4 molecules
• How is a mole described in terms of quantity?


  It is a number like "dozen" or "billion"
• What is the formula to calculate the amount of substance?


  $n =$$\frac{N}{N_A}$
• How can the amount of substance be calculated if the mass is known?


  $n =$$\frac{M}{M_r}$
• What must the molar mass be in if the mass is measured in grams?


  g mol$^{-1}$
• How do you calculate the amount of aspirin in a tablet containing 300 mg?

  Convert 300 mg to grams and use $n =$$\frac{M}{M_r}$
• How do you calculate the mass and amount of sodium pertechnetate in a typical injection?

  Use $n =$$\frac{N}{N_A}$ and then $m =$$n \times M_r$
• How do you calculate the amount of water in sodium sulphate decahydrate?


  Use $n =$$0.5 \text{ mol} \times 10 \text{ H2O}$
• What units are used for volumes of liquids?


  mL and L
• What is the relationship between cm$^{3}$ and mL?


  1 cm$^{3}$ is equal to 1 mL
• What is the relationship between dm$^{3}$ and L?


  1000 cm$^{3}$ is equal to 1 dm$^{3}$ which is equal to 1 L
• What is concentration?


  The quantity of substance per unit volume
• What are typical units for concentration?


  g dm$^{-3}$, mg cm$^{-3}$, mol dm$^{-3}$
• What is amount concentration?


  Concentration measured in moles
• What is the symbol for amount concentration?


  Lower case italic c
• How is molarity defined?


  As mol dm$^{-3}$ or mol L$^{-1}$
• How do you calculate the molarity of a potassium iodate solution?


  Use $c =$$\frac{n}{V}$ where n is the amount in mol and V is the volume in dm$^{3}$
• How do you calculate the molarity of a 0.9% m/v sodium chloride solution?


  Convert 0.9% to grams per volume and use $c =$$\frac{n}{V}$
• What is the difference between amount of substance and concentration?


  Amount is total quantity, concentration is quantity per volume
• How do you calculate the amount of sodium in a 0.1 m sodium sulphate solution?


  Use $n =$$c \times V$ where c is the concentration and V is the volume
• How do you calculate the total amount of sodium chloride when mixing two solutions?


  Add the amounts calculated from each solution
• How do you calculate the glucose concentration in a 25 mL solution?


  Use $c =$$\frac{n}{V}$ where n is the amount in mol and V is the volume in dm$^{3}$
• How is percentage composition commonly expressed in medicines?


  As grams or milliliters of drug per 100 g or 100 mL of medicine
• What is the most common way to express percentage composition?


  On a mass in mass basis
• How do you calculate the percentage of zinc oxide in a paste?


  Use $\frac{\text{mass of zinc oxide}}{\text{total mass}} \times 100\%$
• How do you calculate the percentage mass in volume composition of sodium chloride?


  Use $\frac{\text{mass of sodium chloride}}{\text{volume of solution}} \times 100\%$
• How do you calculate the percentage of chloroform and acetone in a mixture?


  Use $\frac{\text{volume of component}}{\text{total volume}} \times 100\%$
• Why should volume in volume percentage compositions be used for approximate work?


  Because the final volume is rarely equal to the sum of individual volumes
• What is the distinction between a 1:5 ratio and a 1 part in 5 solution?


  A 1:5 ratio means 1 mL of the first component in 6 mL total, while 1 part in 5 means 1 mL in 5 mL total
• What is the purpose of determining stoichiometry in chemical reactions?


  To balance the components on each side of the equations
• What factors affect the efficiency of chemical reactions?


  Reaction conditions, choice of reactants, and properties of starting materials
• What is the limiting reagent in a chemical reaction?


  The reagent that runs out first and limits product formation
• How do you calculate the yield of a reaction?


  By comparing the amount of product obtained to the expected amount
• What does a yield greater than 100% indicate?


  Possible contamination or weighing error