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allthebest

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    May 2017
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    Indonesia

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  1. So the question is: In cats, the allele for curled ears (C) is dominant over the allele for normal ears (c). The allele for black colour (B) is dominant over the allele for grey colour (b). A cross occurs between two cats that are both heterozygous for these unlinked traits. Using a Punnett grid, predict the ratio of phenotypes of offspring in the next generation. I'm so confused about the genotypes and how it should be drawn. A drawing will really help. thank you.
  2. thanks for the clear explanation!
  3. where can I find the answers for inthinking ch.10, 20 and option C? If anyone has it can you please pm me? It'll be a great help. Thanks in advance
  4. I don't understand these P1 questions. Please help me understand them by giving some explanations. answers: 1. B - which equation should be used? I thought it was mol= vol/24 2. A - why is the denominator (0.5)^2? I thought it was C 3. C - I don't get these types of questions. + means a stronger oxidizing agent and - is strong reducing agent. Then shouldn't the most negative one, Fe2+, be the correct answer? 4. C - no idea about this... 5. D - how do you know... 6. A - I know it is optical, but how do we know if it is or is not geometric? Thank you very much. Your help will really help me.
  5. yes, it's from 2014, the old syllabus. It's great to know that it's not from the current syllabus. Thanks for your reply!
  6. What is the major organic product formed from the reaction of (CH3)3CBr with concentrated ethanolic solution of KOH? A. (CH3)3COH B. (CH3)2CCH2 C. (CH3)2CO D. (CH3)2CHO I thought the answer was A because of the nucleophilic substitution reaction of tertiary halogenoalkane by SN1 mechanism. However, the markscheme says it's B Can anyone explain why the answer is B? Thanks in advance
  7. Thank you!! May I ask another question..? The question is: Ammonia, NH3 , can be used to clean ovens. The concentration of hydroxide ions, OH– (aq), in a solution of ammonia is 3.98 × 10–3 mol dm–3. Calculate its pH, correct to one decimal place, at 298 K. and mark scheme: [H O ] (1.00 10 ) 2.51 10 (moldm ) [OH ] (3.98 10 ) K − + − − − − = = × = × × ; ( 12 ) 3 pH = −log[H O+ ] = −log(2.51×10− ) =11.6 ; [2] OR pOH = (−log (5.98×10−3 ) =)2.4 ; pH = (14.00 − 2.40) =11.6 ; Why can't we directly do pOH= -log(3.98 x 10^-3) and then do 14-pOH? Why do we need to use the Kw or why is pOH = (−log (5.98×10−3 )..?? I'd be very thankful if you would answer this questions also. Thank you.
  8. Please help me with this question: Question: 25.0 cm3 of 1.00 × 10–2 mol dm–3 hydrochloric acid solution is added to 50.0 cm3 of 1.00 × 10–2 mol dm–3 aqueous ammonia solution. Calculate the concentrations of both ammonia and ammonium ions in the resulting solution and hence determine the pH of the solution. Mark scheme: initial amount of HCl = × 1.00 × 10–2 = 2.50 × 10–4 mol and initial amount of NH3 = × 1.00 × 10–2 = 5.00 × 10–4 mol; final amount of NH4+ and NH3 both = 2.50 × 10–4 mol; final [NH4+] and [NH3] both = = 3.33 × 10–3 mol dm–3; [OH–] = Kb × = Kb = 10–4.75 /1.78 × 10–5; pOH = 4.75 hence pH = 9.25; I don't quite understand the reactions involving ammonia solution, like are both NH4+ and NH3 are present there? Why do we have to know the final amount of them both and where did it come from? Thank you
  9. Please help me with this question: Determine the pH of a solution formed from adding 50.0cm3 of 1.00moldm-3 ethanoic acid, CH3COOH(aq), to 50.0 cm3 of 0.600moldm-3 sodium hydroxide, NaOH (aq) mark scheme: (initial)[CH3COOH] = 0.500 mol dm–3 and) eqm [CH3COOH] = 0.200 mol dm–3; (initial)[CH3COO–] = 0.300 mol dm–3 and) eqm [CH3COO–] = 0.300 mol dm–3; Allow 0.02 moles and 0.03 moles instead of 0.200 and 0.300 mol dm–3. [H+] = Ka = 1.16 × 10–5 mol dm–3 / pH = pKa + log; pH = 4.94; Award [3 max] for correct final answer if no working shown. I'm not sure where that "(initial)[CH3COOH] = 0.500 mol dm–3 and) eqm [CH3COOH] = 0.200 mol dm-3" came from... any explanations? and this questions is where you add ethanoic acid to NaOH, but why are there no calculations regarding NaOH?? I'm having difficulties with acid and base calculations... an explanation would be helpful. Thank you.
  10. Help me with these questions please! There are quite alot... I'll really appreciate your help! 3. Ans: B How do I know oxygen is the heaviest? Is it because it becomes diatomic? 4. Ans: C No idea about this one 7. Ans: C... I thought this was B since noble gases do not have ions. Why is it C? 18. Ans: A No idea... I know increase in entropy would be increase in gas molecules... but what is this question 27. Ans: B How do I know? (I'm new to acid and base...started recently) 29. Ans: C How do I know...? Thank You
  11. Oh my. if its half life, now I get it. Thanks a lot!!
  12. so for no.20, you're saying the answer is D, aren't you?
  13. I don't still quite get no.20...but you're sure the answer is right, right? how should I compare the slope? and if you would please answer the other 2 question I edited below, please. Thank you
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