I have just completed my A2 chemistry OCR A spec. Here are my thoughts:
For the most part, no, A-Level maths at AS or A2 is completely unnecessary in my opinion.
As long as you are okay with rearranging equations with fractions in them (a higher level GCSE skill), you are familiar with power rules like
Unparseable latex formula:a^b*a^c=a^b^+^c
for Kc etc. and finally some BASIC logarithm rules for understanding the mathematics of what makes a buffer solution ideal (basically
log(1)=0) for the Henderson-Haselbalch relationship you should be okay.
Essentially mathematical common sense! It's chemistry,
most of the maths is rearranging things and other basic skills. If you were talking about physics where you require complex knowledge of differential equations and integrals/ exponents then I would strongly advise maths, but you don't come across those in chemistry at this level.
You'll learn a lot of stuff you don't need for chemistry in maths and plus maths is in my opinion very very hard at A2, it takes a lot of dedication and practice for most to succeed.