can't get the answers for this few questions correct, hope someone can enlighten me =) thks in advance!
1. iron is an essential nutrient for pregnant women. Doctors usually prescribe 350 mg FeSO4 tablets as dietary supplement for pregnant women. H/r it was found that iron tablets can cause poisioning deaths in children as little as 590 mg of Fe2+ can be fatal to a 12.5kg child.
How many 350mg FeSo4 tablets wold it constitute a lethal dose to a 12.5kg child.
ans: 5
2. 25 cm3 of 0.02moldm-3 calcium hydroxide is neutralized by 25cm3 of 0.05 moldm-3 of hcl whats the conc of the salt formed in the resulting solution?
ans: 0.0100moldm-3
3. sample of 0.025 mole of cholride of an element Z was dissolved in distilled water and the solution made up to 500cm3. 12.5 cm3 of the solution reacted with 25cm3 of 0.05moldm-3 of silver nitrate solution.
whats the likely formula of the chloride?
ans: ZCl2
1. iron is an essential nutrient for pregnant women. Doctors usually prescribe 350 mg FeSO4 tablets as dietary supplement for pregnant women. H/r it was found that iron tablets can cause poisioning deaths in children as little as 590 mg of Fe2+ can be fatal to a 12.5kg child.
How many 350mg FeSo4 tablets wold it constitute a lethal dose to a 12.5kg child.
ans: 5
(Fe)2+ + (SO4)2- --> FeSO4
So, 350mg of FeSO4 would give you 0.35/[55.8+32.1+(16)(4)] = 0.002304 mols of FeSO4
Since FeSO4 = (Fe)2+, there is also 0.002304 mols of Fe2+ in the tablet
No. of mols of (Fe)2+ to cause death in a 12.5kg child = 0.59/55.8 = 0.01057 mols
So number of tablets = 0.01057/0.002304 = 4.589
Round it up to 5 since 4 tablets wouldn't be enough to kill.
hope that helps(:
2. 25 cm3 of 0.02moldm-3 calcium hydroxide is neutralized by 25cm3 of 0.05 moldm-3 of hcl whats the conc of the salt formed in the resulting solution?
ans: 0.0100moldm-3
Ca(OH)2 + 2HCl --> CaCl2 + 2H2O
this is the reaction between calcium hydroxide and hydrochloric acid.
so since the question already tells you the respective volumes and concentrations, the only thing you can find is the number of mols.
No. of mols of Ca(OH)2 = 0.025 x 0.02 = 0.0005 mols
No. of mols of HCl = 0.025 x 0.05 = 0.00125 mols
you know that one mol of Ca(OH)2 needs 2 mols of HCl for the reaction to take place. but from what you have calculated, the number of mols of HCl is more than what you need. (you only need 0.0005 x 2 = 0.001 mols)
therefore you CANNOT use 0.00125 to calculate for the number of mols of CaCl2(salt)
Since CaCl2 = Ca(OH)2,
No. of mols of CaCl2 = 0.0005 mols
and the concentration of CaCl2 is therefore 0.0005/0.05 = 0.0100 mol/dm3
i hope that helps too. (:
Charmy has already replied you on Q1.
For Q2, do an ICF (Initial, Change, Final) table. Be careful when calculating molarity, take into account the new volume of solution.
For Q3, calculate molarity, hence no. of moles (???1) of Z-choloride in 12.5cm3. From no. of moles of Ag+ used (???2), deduce no. of moles of Cl- (???2) present. So (???1) no. of moles of Z-chloride contains (???2) moles of Cl- ions. Hence 1 mole of Z-chloride contains (???3) moles of Cl- ions. Therefore, the formula is (???4).
thanks ppl!!! (:
got 2 more qns. 1d i don't understand the qn.
1d. Some of the nitrogen of a fertilizer could be present as nitrate NO3-ions. nitrate ions can be reduced by acidified Fe2+(aq) to form a nitrogen containing product Y. 1 mole of NO3- ions required 8 mole of Fe2+ in this reaction.
(i) Calculate the oxidation no. of nitrogen in the nitrogen containing pdt, Y.
ans: -3
(ii) Hence suggest an identity of the nitrogen containing pdt, Y, formed in this reaction.
ans: NH4+
3c. Element W reacts with chlorine gas to produce a chloride compound WClm. the WClm molecules can form dimers under suitable conditions.
(i) suggest the value of m an give the chemical formula of W
ans: Group 3, m=3, WCl3
(ii) expl why the molecules of W suggested in (i) are capable of forming dimers.
mcq qn 8. The density of CH4 gas at 0 deg celsius and a pressure of 1 atm is 4 times that of gas x at the same temp, which of the following can be gas X?
A) H2
B) He
C) O2
D) C4H16
ans: B
Originally posted by blueftw:thanks ppl!!! (:
got 2 more qns. 1d i don't understand the qn.
1d. Some of the nitrogen of a fertilizer could be present as nitrate NO3-ions. nitrate ions can be reduced by acidified Fe2+(aq) to form a nitrogen containing product Y. 1 mole of NO3- ions required 8 mole of Fe2+ in this reaction.
(i) Calculate the oxidation no. of nitrogen in the nitrogen containing pdt, Y.
ans: -3
(ii) Hence suggest an identity of the nitrogen containing pdt, Y, formed in this reaction.
ans: NH4+
3c. Element W reacts with chlorine gas to produce a chloride compound WClm. the WClm molecules can form dimers under suitable conditions.
(i) suggest the value of m an give the chemical formula of W
ans: Group 3, m=3, WCl3
(ii) expl why the molecules of W suggested in (i) are capable of forming dimers.
mcq qn 8. The density of CH4 gas at 0 deg celsius and a pressure of 1 atm is 4 times that of gas x at the same temp, which of the following can be gas X?
A) H2
B) He
C) O2
D) C4H16
ans: B
Q1.
Calculate the no. of moles of electrons ganied/lost by 1 mole of species, by using stoichiometry of the balanced redox equation. Final O.S. = initial O.S. + electrons gained (-ve value) or lost (+ve value).
The O.S. of N in NH4+ is -3. The question probably gave you a list of N containing species to choose from.
Q3.
Group III elements often lack a stable octet in their compounds. Eg. AlCl3. Which is why Al is willing to accept a pair of electrons from Cl- to form AlCl4-. The reason they form dimers is to enable the atoms to have a stable octet.
Q8.
Density = Mass / Volume. For the same volume (hence moles), methane has a mass of 16g which is 4x greater than the mass of He (4g).