At 20\u00b0C, the water autoionization constant, Kw, is 6.8 \u00b4 10\u201315. What is the H3O+ concentration in neutral water at this temperature? <\/p>\n\n\n\n
A. 6.8 \u00d7 10\u20137 M <\/p>\n\n\n\n
B. 3.4 \u00d7 10\u201315 M <\/p>\n\n\n\n
C. 6.8 \u00d7 10\u201315 M <\/p>\n\n\n\n
D. 8.2 \u00d7 10\u20138 M <\/p>\n\n\n\n
E. 1.0 \u00d7 10\u20137 M<\/p>\n\n\n\n
The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n The autoionization constant of water, ( K_w ), represents the product of the concentrations of hydrogen ions (( H_3O^+ )) and hydroxide ions (( OH^- )) in water. The equation for autoionization is:<\/p>\n\n\n\n [ At equilibrium, the concentrations of ( H_3O^+ ) and ( OH^- ) in pure water are equal. Therefore, we can express the concentration of ( H_3O^+ ) (or ( OH^- )) as:<\/p>\n\n\n\n [ The autoionization constant is given by:<\/p>\n\n\n\n [ At 20\u00b0C, ( K_w ) is provided as ( 6.8 \\times 10^{-15} ). Since the concentrations of ( H_3O^+ ) and ( OH^- ) are equal in neutral water, we can rewrite the equation as:<\/p>\n\n\n\n [ Substitute the value of ( K_w ) at 20\u00b0C:<\/p>\n\n\n\n [ To find the concentration of ( H_3O^+ ), take the square root of both sides:<\/p>\n\n\n\n [ Therefore, the concentration of ( H_3O^+ ) in neutral water at 20\u00b0C is 8.2 \u00d7 10\u207b\u2078 M<\/strong>.<\/p>\n\n\n\n Answer: D. 8.2 \u00d7 10\u207b\u2078 M<\/strong><\/p>\n\n\n\n The ( K_w ) value changes with temperature. At 20\u00b0C, the value of ( K_w ) is lower than at 25\u00b0C, where it is typically ( 1.0 \\times 10^{-14} ). This lower ( K_w ) results in a lower concentration of ( H_3O^+ ) in neutral water at 20\u00b0C. The relationship between ( K_w ) and the concentration of ions is fundamental for understanding the pH of water and its variations with temperature. At 25\u00b0C, the concentration of ( H_3O^+ ) in neutral water would be ( 1.0 \\times 10^{-7} \\, M ), but at 20\u00b0C, due to the lower ( K_w ), the concentration is significantly lower, which is why the correct answer is ( 8.2 \\times 10^{-8} \\, M ).<\/p>\n","protected":false},"excerpt":{"rendered":" At 20\u00b0C, the water autoionization constant, Kw, is 6.8 \u00b4 10\u201315. What is the H3O+ concentration in neutral water at this temperature? A. 6.8 \u00d7 10\u20137 M B. 3.4 \u00d7 10\u201315 M C. 6.8 \u00d7 10\u201315 M D. 8.2 \u00d7 10\u20138 M E. 1.0 \u00d7 10\u20137 M The Correct Answer and Explanation is: The autoionization […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[25],"tags":[],"class_list":["post-165370","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/165370","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/comments?post=165370"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/165370\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=165370"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=165370"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=165370"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
H_2O \\rightleftharpoons H_3O^+ + OH^-
]<\/p>\n\n\n\n
[H_3O^+] = [OH^-]
]<\/p>\n\n\n\n
K_w = [H_3O^+][OH^-]
]<\/p>\n\n\n\n
K_w = [H_3O^+]^2
]<\/p>\n\n\n\n
6.8 \\times 10^{-15} = [H_3O^+]^2
]<\/p>\n\n\n\n
[H_3O^+] = \\sqrt{6.8 \\times 10^{-15}} = 8.2 \\times 10^{-8} \\, M
]<\/p>\n\n\n\nExplanation:<\/h3>\n\n\n\n