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Water with a low pH can be described as "acidic" water. How would you refer to water with a high pH?

I would guess it's "alkalitic" or "alkalinic," but I can't find any references to those words at Dictionary.com.

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    What was wrong with alkaline?
    – stevesliva
    Aug 5, 2015 at 4:21
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    I'd use "alkaline". "Basic" might be technically correct but is confusing.
    – Hot Licks
    Aug 5, 2015 at 13:01
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    @HotLicks 'Basic' is one of those words which translated to many other languages are less confusing. In English you're completely right.
    – Mast
    Aug 5, 2015 at 16:18
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    Is "basic" too basic for you? Aug 5, 2015 at 18:31
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    Growing up as a Detroit Tigers fan, I always wondered why chemists were so obsessed with Al Kaline, or why they named batteries after him. Aug 5, 2015 at 19:10

6 Answers 6

50

The commonly used antonym of acid is alkali, of acidic is alkaline. As you mention, acid/acidic refer to pH less than 7, alkali/alkaline to pH greater than 7, and neutral to pH equal to 7. In a long scientific career I have never met the term alkalitic and extremely rarely the term alkalinic.

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  • So acid is to a alkali, as acidic is to alkaline? I guess I've just always wrongly assumed that the opposite of acid is alkaline. alkaline just sounds.. wrong though
    – cantsay
    Aug 6, 2015 at 3:07
  • I went with this as the answer due to the definitions by Oxford - Alkaline "Having the properties of an alkali, or containing alkali; having a pH greater than 7" - Basic "Having the properties of a base, or containing a base; having a pH above 7" - Alkaline seems to be more the opposite of acidic (if you think of acid being one side of neutral and alkali being the other)
    – cantsay
    Aug 6, 2015 at 3:23
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    @cantsay not all bases are alkalis, all alkalis are bases, all bases have pH above 7 in aqueous solutions. However, "acidic water" and "alkaline water" are set expressions used in a recent pseudoscience movement, so it would be the correct antonym in that context.
    – Cubbi
    Aug 6, 2015 at 17:55
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    Bear in mind, though, that acid is commonly used as an adjective, both literally ('acid rain') and figuratively. The opposite then would be alkaline in the chemical sense (in the metaphorical sense, I would imagine sweet). Aug 6, 2015 at 22:45
51

"Basic" is the term for substances that are bases, opposite to substances that are "acidic", or acids.

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  • That's true, I had forgotten that... But we did use alkalinic also. Aug 5, 2015 at 4:26
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    @LamarLatrell "alkalinic" isn't a word. At least, it's not in any of the dictionaries I checked. It picks up some Google hits from people who use it to describe soils and foods, but it seems to be a mistaken attempt to turn "alkali" into an adjective. The accepted term is "alkaline". Aug 5, 2015 at 14:14
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Strong bases can be described as Caustic. In Chemistry the word is reserved for those bases 'capable of burning, corroding, or destroying living tissue'. Although Basic and Alkaline are opposites of acidic as well, sometimes the stronger term is used for extra effect.

Here's a Google Ngram comparing the prevalence of caustic to alkaline, and two obscure terms from other answers: alkalic and alkalinic.

Google ngram comparing caustic to alkanic+alkalinic

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    Alkaline, not alkalic. "Alkalic" is a term in geology meaning a rock that's richer in sodium or potassium than normal. Aug 5, 2015 at 22:03
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    @DavidRicherby Eh, I'm not sure how that snuck in there, I took over bad habits from the answers here.Updated the ngram to include the general term for alkaline.
    – Spork
    Aug 5, 2015 at 23:00
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    That graph is probably at least somewhat skewed by alkaline batteries.
    – DevSolar
    Aug 6, 2015 at 14:13
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    Strong acids can also be described as caustic, which means capable of corroding living tissue (see merriam-webster.com/dictionary/caustic).
    – Marconius
    Aug 6, 2015 at 23:49
  • @Marconius yeah.. somehow I have learnt that caustic only refers to bases, but it seems to be used more generally. Wikipedia: 'Sometimes the word 'caustic' is used as a synonym but 'caustic' generally refers only to strong bases, particularly alkalis, and not to acids, oxidizers, or other non-alkaline corrosives'
    – Spork
    Aug 7, 2015 at 1:57
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Alkaline or basic are the words to describe water with a high pH (That's how we've always described substances with a high pH in all my chemistry classes)

However, if you feel like you need an antonym with a closer equivalent to 'acidic' try alkalic

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    Scroll to the British Dictionary definition
    – Aaron
    Aug 5, 2015 at 5:07
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    I suggest that you do not try alkalic, unless you clearly hear several of your profs or supervisors use that term. Which I doubt you will.
    – ab2
    Aug 5, 2015 at 18:20
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    I've never heard "alkalic" used in the context of chemistry, even in the UK. Aug 5, 2015 at 22:05
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    I am sorry to say that in a long scientific career covering many aspects of chemistry, physics and other branches of science I have never encountered the word "alkalic".
    – Anton
    Aug 6, 2015 at 19:56
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The word opposite of acidic would be basic.

A SOLUTION with low pH is considered acidic. A solution with a high pH is considered basic. Conversely, a solution with a low pOH is considered basic. A solution with a high pOH is considered acidic.

Alkalinity is not the same property as basicity. Basicity describes the ratio of concentrations of H3O+ to OH- in a soution. Alkalinity describes a solution's ability to neutralize H+, regardless of pH/ pOH.

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    Supporting sources?
    – David
    Sep 19, 2016 at 21:49
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The opposite of acidic is basic. Anything on the scale from 1-6 is acidic, and anything form 8-14 is basic

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