some questions

hi can anyone please help me with these chemistry questions. please!! ive written what i think the answer is is in bold.thanks!

1) which contains more molecules: 1 mol of CO or 1 mol CO2? CO2

2) How many moles are there in 1 teaspoon (10mg) of antacid, Al(OH)3 (Mr=78.0)?0.128moles

3)The density of ethanol is 0.79 gcm-3 and has an Mr of 46.1. How many moles are present in 100cm3? 0.017moles

4)Calculate the molar concentration (molarity) of 0.50mol glucose dissolved in 0.2L of solution? 2.5

5) A solution of collagen (Mr=280 KD), is made to a concentration of 20mg ml-1. What is the molar concentration (molarity)?

6) A patient recieves 2.0g NaCl intravenously over 8 hours. What volume of a 0.50% (m/v) NaCl solution was delivered? 400cm3

7) Calculate the mass needed to prepare 1500ml of 0.2M NaCl.

8) Calculate the mass of noradrenaline (Mr=337.3) required to make up 25cm3 of a 3 x 10-4 moldm-3 solution.

You are measuring the absorbance of a solution of haemoglobin (Hb) using a spectrophotometer in order to determine the concentration, but the reading is off-scale. You must dilute te solution in order to obtain a reading that is on the scale.

9) What volumes of Hb and buffer would you mix in order to prepare 10cm3 of a 2-fold dilution?

10) What volumes of Hb and buffer would you mix in order to prepare 10cm3 of a 1:2 dilution?

11) you calculate the concentration of Hb in a 1:9 solution to be 5.6 x 10-5 M. What was the concentration of the undiluted Hb.

12) You add 50 microlitres of an enzyme solution(concentration 20mM) to the substrate to begin a reaction. The final volume of the reaction mixture is 2.5ml. What is the concentration of enzyme in the reaction mixture?

THANKS!!! :smile:

Reply 1

firestone

1) One mole of anything contains the same number of particles (not atoms) of whatever that one mole is of as one mole is defined as 6.02x10²³. So 1 mol of CO and carbon dioxide contains the same number of molecules.

2) 10mg = 0.01g, so if 1 mol of antacid weighs 78g (molar mass) then 0.01g would be 1/(78/0.01) = 1.28x10^-4 mol (3s.f.). Remember to convert the units to grams at the beginning.

3) If 1cm³ weighs 0.79g, 100cm³ weighs 79g. 1mol of ethanol weighs 46.1g, so 79g would be 79/46.1 = 1.71mol.

4) I agree with you.

5) 20mg in one ml, 1l = 1000ml = 1000cm³ = 1dm³. So 20,000mg = 20g in 1dm³. 1g weighs...not sure what 1KD is. :redface:

Sorry! No idea.

6) I'm almost certain that I've done this completely wrong because my value looks a bit...But anyway, I got that the molar mass of NaCl is 58.5gmol^-1, so 2g in total would be 2/58.5 = 0.034188034 mol. Not sure what is meant by a 0.50% concentration but does this mean that the concentration of the sodium chloride solution is 0.005 moldm^-3? If so, 0.005 = 0.034188034/volume in dm³, volume delivered in dm³ = 0.034188034/0.005 = 6.837606838...dm³ = 6838cm³.

7) 0.2M of NaCl is 0.2moldm^-3. 1500ml = 1.5litres = 1.5dm³. So for 1.5dm³, 0.2x1.5 = 0.3mol of NaCl is required. 1 mol of NaCl weighs 58.5g, so 0.3mol weighs 0.3x58.5 = 17.55g.

*I think.
Apologies in advance for any questions that I've done wrong! :redface:

Reply 2

Eau

Here's my input:

Q1-3: I agree with firestone.

Q4: I agree with both of you. (Remember the units of concentration is 2.5 mol.dm^-3 or M.)

Q5: I've never seem KD either, but I'm assuming it's a multiple of 280, as collagen would have quite a high Mr.

Assuming KD is a multiple:

Concentration of collagen is 0.02/0.001 = 20 g/dm^3

So molar concentration will be 1/14 KD^-1 mol/dm^3

(My best guess here.)

Q6: I think I agree with OP. 0.5/100 * x = 2.0 g => x = 400 g. And since the density of saline solution is close to 1, 400 cm^3 would be close enough.

Q7: I agree with firestone.

Q8: Firstly, find the amount in 25cm^3 of a 3 * 10^-4 moldm-3.

So, 3 * 10^-4 * 25/1000 = 7.5 * 10^-6 mol

Mass = 7.5 * 10^-6 * 337.5 = 2.53 * 10^-3 g

Before anyone does all the questions for you, it's better if I give you the formulae and tips on these questions.

Amount/mol = {Mass/g}/{RMM/g.mol^-1}

Concentration/mol.dm^-3 = {Amount/mol}/{Volume/dm^3}

You can reaarrange these formulae to get the answer you need. Remember to input the correct units though.