Go back to Nicholas's IPA Machine 
s
English spelling of the IPA s sound: The letter s as in "ask", or a soft c as in "nice".
Note: The English letter s usually makes the IPA s sound, but sometimes it makes the IPA z sound (as in the word "using") or the IPA ʒ sound (as in the word "usual"). In a few cases it makes the IPA ʃ sound as in "version" or "passion").
Words where the IPA s sound is spelled with a letter s or ss
house, first, answer, save, base, must, soon, also, list, sort, similar,
sports, toast, aspect, artist, forest, customs, disappear, rescue
assume, less, lesson, across, access, assert, boss, happiness
Words where the IPA s sound is spelled with a soft c
nice, place, face, dance, police, city, citizen, centre, receive, circle, cycle, trace,
resource, deception, centimetre, celebrate, inspire, tolerance, office, practice
Words where the IPA s sound is spelled with sc
science, scientist, adolescent, ascent, descent, abscess, crescent, scene, scent, fascinate, scimitar, scissors, disciple, discipline, miscellaneous, scythe, isosceles, luminescence, muscle, corpuscle, etc.
(Note: The c is usually silent in sce, sci, scy and scl but it is not silent in sca, sco, scr or scu. For example: Scar, scout, discount, discover, disco, abscond, Scottish, rescue, describe, script, transcript, screen, misconception, landscape, ascorbic, vascular, auscultation, sclera, etc)
Plurals and possessives
The rules are the same for saying the plural s (as in "two cats and two dogs)" and the apostrophe s (as in "the cat's bed and the dog's bone" or "cats' and dogs' owners").
If the word ends in a c, f, k, p or t then a plural or apostrophe s makes the IPA s sound (as in "Jack's book" or "the cat's bed"). If the word ends in any other letter, then a plural or apostrophe s makes the IPA z sound (as in "John's book" or "the dog's bed").