The difference between 'untuk' and 'kepada'

This post about the difference between 'untuk' and 'kepada' is written in responce to a query by a reader of this blog.

Both 'untuk' and 'kepada' are 'kata sendi nama' (prepositions).

The equivalent of 'untuk' in English is 'for'. Hence you can make sentences such as the following:
1 Hadiah ini untuk awak. [This gift is for you.]
2 Saya membeli sebuah buku untuk adikku. [I bought a book for my brother.]
3 Buku bertompok merah ini untuk rujukan di dalam perpustakaan sahaja. [This red-spotted book is for reference in the library only.]
Notice that 'untuk' is considered a preposition if it is used in front of nouns. If it is used in front of a verb, then it is a 'kata hubung' (conjunction) In the sentence below, 'untuk' is used as a conjunction.
Dia pergi ke farmasi itu untuk membeli ubat. [He went to the pharmacy to buy medicine.]

As for 'kepada', it is the equivalent of 'to' in English. Here are some examples of how 'kepada' is used in sentences.
1 Saya memberikan buku itu kepada Ali. [I gave the book to Ali.]
2 Warna lampu isyarat lalu lintas bertukar daripada merah kepada hijau. [The traffic lights changed from red to green.]
3 Kepada siapakah harus saya adukan hal ini? [To whom should I complain about this matter?]
4 Harga sepiring mi goreng naik daripada dua ringgit kepada dua ringgit setengah. [The price of a plate of fried noddle has increased from two ringgit to two and a half ringgit.] (In this case, daripada .... kepada is a pair for showing 'julat' (range, such as from small to big, from 2% to 3% etc.)
The preposition 'kepada' is usually used in front of nouns denoting living things, except for the pair of daripada ... kepada which shows a range.