Chemistry Questions

Question

1. If a diluted saline solution was 20 v/v% and you poured out 200mL, what amount (mL) of it would actually be the solute?

2. What is the molar concentration of chloride ions when 50 grams of lead (II) chloride is dissolved in 400mL of water?

3. A 45kg person drinks water that’s contaminated with lead. It is found that they have 42ppm of lead in their body. How much (mg) of lead is actually present?

4. A chemist creates a new drug for allergies. To put it into tablet form, the drug is placed in a 35 m/m%. If each tablet is to consist of 50mg of the drug, how much does the tablet weigh (mg)?

Answer 1

1.) You can't really have a 20% v/v solution of saline because saline is NaCl which is a solid and volume/volume % solutions are used when pure solutes in liquid form are used. So, solutions of NaCl (saline) are always given as % w/v or % w/w. And how can you ask what amount in ml would actually the the solute since ml is a measure of volume and the solute, NaCl, is a solid, so it would be measured in grams, not mls.

2.) 50 g PbCl₂ x 1 mol PbCl₂/278 g x 2 mol Cl/mol PbCl₂ / 0.4 L = 0.899 M Cl^-

3.) 42 ppm Pb = 42 mg Pb/kg body weight

42 mg/kg x 45 kg = 1890 mg of lead

4.) If by m/m% you mean mass/mass which is the same as w/w %, then we have the following:

50 mg / x mg = 0.35 and x = 143 mg total mass of tablet.

To check this, if we have 50 mg of drug and the total mass of the tablet is 143 mg, what is the m/m percent of the drug? It will be 50 mg/143 mg (x100%) = 34.9 % m/m