CHEM AND BIO HELP AND TIPS HERE

[Moonlyte]

Hmm... possible. Here are the exact wordings:

i see...the question surely is confusing....

By the way...can the marking scheme be wrong?

[thenewkid™]

Hmm... possible. Here are the exact wordings:

sry
didnt see u hd answered

[Burhan.arshad]

When added to 20 cm3 of 0.5 M sulphuric acid, which substance would give a neutral solution?
A 20 cm3 of 0.5 M sodium hydroxide
B 10 cm3 of 0.5 M sodium hydroxide
C 40 cm3 of 1.0 M sodium hydroxide
D 20 cm3 of 1.0 M sodium hydroxide

anxer is d.......but how? i think it's a

[Vin]

heyy .. exams 2mrrw wish everyone luckk ..

my question is from may/june 2003 it sayss

a)explain why in some parts of the world, not enough food is available to feed the people living there . (10 marks)

b) describe the use of hormones in foood production

thannks in advance !!!

y dont u hav a look at the ms .. ?? if u still wan it tell ..

[NidZ- Hero]

can any1 explain how HIV affects the immune system .

[nid404]

The molar ratio has to be seen.
Reaction is

H₂SO₄+ 2NaOH--->Na₂SO₄

Ratio of moles is 1:2

no of moles of sulphuric acid= 0.5 X 20/1000= 0.01

so no of moles of NaOH= 0.02 (twice)

vol of NaOH= 20/1000 dm3
conc= 0.02 X1000/20 = 1 M

Hence D

Try it with the other options...either the vol of conc will not tally with the no of moles.

[ambitious94]

Hmm... possible. Here are the exact wordings:

Spermicides is another example of a chemical method. It says so right here in my study guide. The contraceptive pill and spermicides.
Hey...progesterone also prevents the implantation of a bastula (in the guide too).....although I dunno how :S

[J.Darren]

Ether is a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether" (CH3-CH2-O-CH2-CH3). Ethers are common in organic chemistry and pervasive in biochemistry, as they are common linkages in carbohydrates and lignin.

Try going to the following links to find what specific areas you want answers in.

Chemical properties of ether
Preparation of ethers
Friedel craft reaction
Halogenation of ether
Hydrolysis of ether
Oxidation of etherEster is formed when alkanoic acid and alcohol reacts under heat, concecentrated sulphuric acid amd catalyst. The COO linkage present in ester is also known as the ester linkage.

For example if methanol and ethanoic acid reacted together, the product would be called methyl ethnoate. When drawing the structure, draw the alkanoic acid first (from left to right), the COO linkage and finally, the alcohol.
Peroxide formation
Ring substitution in aromatic ethers
Salt formation by ether
Williamson synthesis

[J.Darren]

The molar ratio has to be seen.
Reaction is

H₂SO₄+ 2NaOH--->Na₂SO₄

Ratio of moles is 1:2

no of moles of sulphuric acid= 0.5 X 20/1000= 0.01

so no of moles of NaOH= 0.02 (twice)

vol of NaOH= 20/1000 dm3
conc= 0.02 X1000/20 = 1 M

Hence D

Try it with the other options...either the vol of conc will not tally with the no of moles.

Although not essential, but it might be a good idea to include the H2O as well ...

[nid404]

Although not essential, but it might be a good idea to include the H2O as well ...

woopsy 

[ambitious94]

can any1 explain how HIV affects the immune system .

As far as I know, and I'd appreciate if people would add to it:
The virus attacks the lymphocytes, which act as host cells for these viruses, and replicates its DNA into the nucleas of the lymphocytes, so that they are unable to produce antibodies. In this way these cells are unable to produce an immune response, and so the antibody production part of the immune system is 'deactivated'.

[saleemsamer]

Hey guys
i kno i have mark schemes but can some1 plz give me a model answer for O/N 05 p3 q6 c (biology) PLZ
it says ref. and ref. i kno wat it means but i wud like a full answer
thx in advance

any1??

[nid404]

any1??

Paper plz

[Syed Kazim]

heyy .. exams 2mrrw wish everyone luckk ..

my question is from may/june 2003 it sayss

a)explain why in some parts of the world, not enough food is available to feed the people living there . (10 marks)

b) describe the use of hormones in foood production

thannks in advance !!!

A.

• Unsuitable climate, temperate, rainfall or relief. Can also be caused due to pollution.
• Natural disasters.
• Poor soil or lack of inorganic ions or fertiliser.
• War or farm redistribution.
• Farmers poorly educated.

B.

• Auxin
• To promote root and shoot formation
• Used with cattle to increase milk production
• Used to increase meat production
• Sprayed onto flowers to induce fruit production

This is the mark scheme.

[ambitious94]

any1??

The enzymes are extracted from microorganisms such a bacteria or fungi which are fermented in a fermentation vessel. There is a pipe to add feedstock, an air pipe to blow in air to supply oxygen for the microorganism to respire, and a stirrer to stir the mixture. The process is kept at a temperature of 26 degrees Celsius, at a pH of 5-6. Extracellular enzymes are extracted by filtering them from the feedstock, and intracellular by crushing the microorganisms, then adding water and filtering the mixture so that the enzymes are in solution.