1、一般地形容酸气信中味，两者可通用。2、acid可作名词，sour不行。3、acid可形容土壤（主要是化学概念上的酸），sour主要形容食物；4、就引申义说，acid形容滑塌山说话尖刻；sour形容不友好的’关系、眼神‘等acid (LIQUID SUBSTANCE) 可作名词 noun [C or U]，意为’any of various usually liquid substances which can react chemically with and sometimes dissolve other materials:例如：Vinegar is an acid.醋是一种酸。.acid 也可作形容词 adjective，有两种意思：1. ‘containing acid, or having similar qualities to an acid':例如：an acid taste/smell 酸的口味/气味；acid soil酸性土壤（这里不能用sour）第二个意思用来形容衫携尖刻的说话方式2. 'describes a remark or way of speaking that is cruel or criticizes something in an unkind way':例如When she spoke her tone was acid她说话时语气很尖刻。sour 只能作形容词：adjective有两个意思：1. 主要是形容食物的酸味酸气：'having a sharp, sometimes unpleasant, taste or smell, like a lemon, and not sweet: 例如：These plums are a bit sour.这些李子有点酸。2. 不友好的恼人的，'unfriendly or easily annoyed':例如：Overnight, it seemed, their relationship had turned sour.过了一晚上似乎他们的关系变糟了。She gave me a sour look.她朝我不友好的看了一眼。参考：Cambridge Learner's Advanced Dictionary
