A buffer is usually composed of either:
- a weak base combined with its conjugate acid, or
- a weak acid combined with its conjugate base
Now, examining each of the choices:
1- KOH and NH3: since they are both bases, thus this mixture is not a buffer
2- HBr and NaCl: since HBr is a strong acid while NaCl is the salt of another different acid, thus this mixture is not a buffer
3- HCl and HBr: these are both considered to be strong acid, thus this mixture is not a buffer
4- HCHO2 and NaCHO2: as for HCH02, it is considered a weak base while NaCHO2 is considered its conjugate base, thus this mixture is a buffer
The 3 parts are
1) A five carbon ribose sugar
2) A Phosphate molecule
3) The four nitrogenous bases
I hope that's help !
this equation is balanced.
10) In order to find the conjugate acid of a chemical you just add a hydrogen to the chemical.
examples: the conjugate acid of Cl⁻ is HCl, the conjugate acid of PO₄³⁻ is HPO₄²⁻, the conjugate acid of NH₃ is NH₄⁺, the conjugate acid of HCO₃⁻ is H₂CO₃, and the conjugate acid of H₂O is H₃O⁺
To find the conjugate base of a chemical you just reverse that process (take away a hydrogen).
examples: the conjugate base of H₂SO₄ is HSO₄⁻, the conjugate base of CH₃COOH is CH₃COO⁻, the conjugate base of H₃PO₄ is H₂PO₄⁻, and the conjugate base of H₂O is OH⁻.
When you identify conjugate acids and bases in a reaction you look to see what lost a proton and what gained a proton. The chemical that gave up the proton acted as an acid and produced a conjugate base while the chemical that accepted a proton produced a conjugate acid.
Example: HCl+NaOH⇒NaCl+H₂O The acid is HCl and its conjugate base is Cl⁻ while NaOH was the base and H₂O is the conjugate acid. (you can ignore the sodium since it is a spectator ion).
11) When completing acid base reactions, need to identify the acid and the base since the acid will give a proton the base creating a conjugate base of the acid and conjugate acid of the base. (You need to balance the equation after you determine what the products will be)
example: H₂SO₄+2NaOH⇒Na₂SO₄+2H₂O (SO₄²⁻ is the conjugate base of HSO₄⁻ which is the conjugate base of H₂SO₄. HSO⁻ is created with the first NaOH molecule and then SO₄⁻ is created with the second NaOH.)
12) All acid base reaction form a salt consisting of the cation from the base and anion from the acid.
examples: NaCl could have come from NaOH reacting with HCl. K₃PO₄ could have come from KOH and H₃PO₄.
13) I don't really know how you are supposed to solve it with out knowing the Ka value of H₂S. H₂S is a weak acid and therefore will not dissociate completely in water so the only way of being able to find the concentration of H⁺ ions that dissociate is knowing the Ka value of H₂S and using ice tables. (Ka=[H⁺][A⁻]/[HA] and is basically the equilibrium constant for the acid when put into water where A⁻ is the conjugate base and HA is the acid).
14) Ca(OH)₂ is a strong base and will therefore dissociate completely in water. That means that when you find the concentration of OH⁻ in solution you can multiply that by the volume of the solution (in liters) to find the number of moles of OH⁻. Then you can divide that by 2 to find the number of moles of Ca(OH)₂ needed. pOH=14-pH which means that pOH=4.2. [OH⁻]=10^-pOH which means [OH⁻]=6.3x10^-5 M. 6.3x10^-5Mx3.00L=1.89x10^-4mol OH⁻ which means that (1.89x10^-4)/2=9.46x10^-5mol Ca(OH)₂.
I hope this helps. Let me know if anything is unclear.
