Calculate the volume (in ml) of 0.170 m naoh that must be added to 389 ml of 0.0543 m 3-(n-morpholino)propanesulfonic acid (mops) to give the solution a ph of 7.55. the pka of mops = 7.18.

3-(n-morpholino)propanesulfonic acid [MOPS] is used as a buffer specially in biological systems

When we add NaOH to it , it forms salt with it and there is a change in the pH of the solution

MOPS + NaOH ---> NaMOPS + H₂O

The Hendersen equation for estimation of pH of a buffer is

pH = pKa + log[salt]/[acid]

7.55 = 7.18 + log[salt]/[acid]

On solving

[salt] / [acid] = 2.344

moles of salt required = 2.344 X moles of acid

initial moles of acid present = 389 X 0.0543 = 21.12 mmoles

let the moles of base added = x mmol

As per equation each mole of base will react with one mole of MOPS

Therefore

moles of salt formed = x mmol

moles of acid left = 21.12-x

x = 2.344 (21.12-x)

x = 49.51 - 2.344x

x = 14.80 mmol

this is the millimoles of base required

So the volume of NaOH needed (mL) = moles / molarity = 14.80/0.170 = 87.05 mL

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.