Chromium (Cr) is a transition element in d block. Chromium has different oxidation states +2, +3 , +6. The oxidation state +6 has strong oxidizing ability. Chromium hydroxide shows amphoteric characteristics. Chromate (CrO42-) & dichromate Cr2O72-) ions are strong oxidizing agents. Chromium is used to make alloys and in electroplating.

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In this tutorial, we study about followings of chromium metal & chromium ion.

Some reactions và characteristics of chromium – we study these things before testing Cr3+ ion because they are important in understanding Cr3+ testing experiments. Test for chromium ion


2 Reactions of chromium và compounds3 Chromium +3 oxidation state6 chạy thử for chromium ion 8 Uses of chromium và its compounds

Electrons configuration of chromium

1s2 2s2 2p6 3s2 3p6 3d5 4s1

READ: hòa tan M Gam hỗn hợp Feo Fe(Oh)2 Feco3 Fe3O4 vào Đó Fe3O4 chỉ chiếm 1/4 tổng cộng Mol lếu Hợp

Major oxidation states of chromium

+2 : 2+(aq) +3 : Cr(OH)3(s) +6 : CrO3(s), Na2Cr2O7

Properties of chromium metal

A silvery blue metal. Much resistance lớn atmospheric corrosion and decay. Readily dissolve in acids to form +II oxidation state. Compounds of +III state occur with oxygen, sulfur and halogens. Mật độ trùng lặp từ khóa of Cr : 7.20 g cm-3 Melting and boiling points Melting point : 18900C Boiling point : 24800C

Reactions of chromium & compounds

Chromium và dilute acids reaction

Chromium react with dilute HCl or dilute H2SO4 to form 2+(aq) blue colour coordination complex.

Chromium và dilute HCl reaction

Chromium reacts with dilute HCl & form, hydrogen gas with chloride ion.


Chromium và dilute H2SO4

As with dilute HCl, chromium reacts with dilute H2SO4 & form hexaaquachromium(ii) ion, hydrogen gas with sulfate ion. Aqueous solution is blue colour.


2+(aq) complex oxidizing behavior

Hexaaquachromium(ii) ion 2+(aq), easily oxidises khổng lồ Cr3+ions by oxygen under atmospheric conditions.


Chromium +3 oxidation state

Most stable oxidation state of Chromium is +3.

Aqueous Chromium(III) ion with alkali reactions

3+(aq) changes its colour (blue-violet) to dark green by forming Cr(OH)3(s) precipitate with alkali. With excess alkali, precipitate dissolves & green colour aqueous 3-(aq) complex is given.


Cr(OH)3, this hydroxide is an amphoteric compound.

Chromium 3+ ion & zinc amalgam

Cr3+ can be reduced to lớn Cr2+ by zinc amalgam. Zinc amalgam is used in clemmensen reduction lớn reduce aldehyde và ketone lớn alkanes.


Chromium +6 oxidation state

Aqueous Cr3+ ions can be oxidized khổng lồ chromate(+6)oxidation state by H2O2 in the presence of alkali.


Equilibrium of chromate ions and dichromate ions

Chromate(+6) ions undergo following equilibrium in acidic medium to khung dichromate ( Cr2O72- ).


Reactions summary of chromium và compounds


Test for chromium ion

Here we discuss some experiments to test Cr3+ ion presence in different compoundsunder qualitative analysis. Chromium forms colourful precipitates & solutions with other elements. Therefore we use those colours, precipitates to lớn identify chromium ion.

Aqueous ammonium sulfide & Cr3+ solution reaction

Addition of aqueous ammonium sulfide ( (NH4)2S(aq) ) lớn Cr3+(aq) solution forms a Cr2S3 precipitate. It quickly hydrolyzes khổng lồ Cr(OH)3(s) which is a green precipitate.


Ammonia và salts of weak acids such as sodium carbonate ( Na2CO3 ) ,ammonium sulfide ( (NH4)2S ) also precipitates Cr3+ ions as chromium hydroxide ( Cr(OH)3 ). This precipitate somewhat soluble in excess aqueous ammonia solution.

NaOH and chromium ion reaction

Aqueous chromium ion reacts with NaOH & form chromium hydroxide, green precipitate which has amphoteric characteristics.Chromium hydroxide will dissolve in excess aqueous NaOH và give green solution by forming sodium hexahydroxychromium(III).

How to lớn identify chromium hydroxide và nickel hydroxide? – video

NaOH, Na2O2 & Cr3+ solution reaction

Addition of NaOH, Na2O2 lớn Cr3+ solution forms Na2CrO4, a yellow solution. Further addition of acetic acid ( CH3COOH ) & BaCl2, a yellow precipitate BaCrO4 is obtained. BaCrO4 is insoluble in acetic acid, but soluble in HNO3 acid.

Ammonium buffer mixture with Cr3+

Cr3+ is completely precipitated as Cr(OH)3 by ammonium buffer solution ( NH4OH / NH4Cl ). Cr(OH)3 is a green precipitate.

Formation of sparingly soluble salts of CrO42-

The anion CrO42- forms sparingly soluble precipitates with Pb2+ , Ag+ , Ba2+. This can be used khổng lồ detect and separate chromates.

PbCrO4: yellow BaCrO4: yellow Ag2CrO4: Brick red

Uses of chromium & its compounds

Chromium(IV) oxide ( CrO2 )

In magnetic recording tapes for better resolution & high frequency response.

Chromium(III) oxide (Cr2O3)

In abrasives, refractory materials, & semiconductors, as a green pigment, especially for colouring glass when chemical and heat resistance are required

Chromium(VI) oxide (CrO3)

Chromium plating, Copper stripping as a corrosion inhibitor in photography

Sodium dichromate (Na2Cr2O7)

Leather tanning, textile manufacture, metal corrosion inhibitor

More to learn about Cr3+ ion

CrPO4 is a greenish precipitate. Cr3+ ions can be oxidized by KMnO4, (NH4)2S2O8 in acidic solutions.


Reaction of chromium with sodium hydroxide

Chromium does not react with aqueous sodium hydroxide. But chromium oxide & chromium hydroxide react with aqueous sodium hydroxide because they have amphoteric characteristics.

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What is the chromium and halogens reaction?

Chromium metal reacts with the halogens to size chromium(III) halides. As an example, chromium reacts with chlorine gas lớn give chromium(III) chloride.

Related Tutorials lớn Chromium ion Test

Chloride ion testing Amphoteric elements, metals, compounds – các mục of amphoteric compounds Metal characteristics of periodic table Alkali earth metal chemistry Solubility if inorganic Compounds, s,p,d block elements Alkali metals chemistry Identify cations by precipitating Precipitates compounds colours Sodium Carbonate Manufacturing Process Solubility of metal hydroxides

Lewis structures

P2O5 lewis structure OH- lewis structure Ammonium ion (NH4+) lewis structure H2CO3 lewis structure

Qualitative Analysis for anions and cations

Organic Chemistry Problems and Answers

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