Explain why ink is a mixture instead of a substance.

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Karyth Cara | College Teacher | (Level 1) Senior Educator

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All matter can be placed into two categories - pure substances and mixtures [of pure substances]. ... The substances in a mixture are not chemically combined, so therefore they can be separated through some physical process. (Florida Institute for Human and Machine Cognition (FIHMC))

To understand whether ink of any sort is a mixture or a substance, first know that substances exist in a pure form while mixtures are combinations of substances.

Pure substances are either [molecular] elements or [molecular] compounds, and mixtures [of pure substances] can be classed as suspensions, solutions, or colloids. (FIHMC)

Since mixtures can be separated into their individual constituent parts, mixtures can be tested by paper chromatography to separate and identify the combined pure substances comprising the mixture. Paper chromatography can be applied to ink to determine if it is a pure substance or a mixture of pure substances (in which two or more pure substances are combined).

Many mixtures, such as inks ... consist of two or more dyes. To separate the dyes, a small portion of the mixture is placed onto an absorbent material, such as filter paper [with] a solvent ... [if a] dye in the ink doesn't dissolve as well, it will not move as far [as another dye]. (FIHMC)

Since, when tested with paper chromatography, ink separates into its constituent pure substances, ink is a mixture.

History of Ink

Dating back to 3,200 B.C, an ink mixture has been in use since Egyptian times when the ink mixture was made from soot and vegetable gum, which held the soot together in a soluble base.

vegetable gum, n.: a powder or resin that is a gelling agent, binding agent, or thickener

Egyptians and Greeks substituted iron oxide in the mixture, which is commonly called rust, to make red ink to use instead of soot-black ink. The Chinese around 2,000 B.C. used alternate methods of mixing black and red inks by using iron sulfur for black mixed with sumac tree sap, which is a vegetable gum, and mercury sulfate for red mixed with sumac tree sap. Egyptians, Greeks and Chinese formed their ink mixtures as solid blocks or sticks that were then mixed with water to use as a liquid ink mixture.

Europeans did not formulate ink mixtures until the 1600s when they used tannic acid from tree bark in mixture with iron salt. This formula produces blue and black ink mixtures.

tannic acid, n.: pale-yellow to light-brown amorphous substance in the form of powder, flakes, or a spongy mass (Encyclopedia Britannica)

Inks were applied using pens, the earliest of which were hollow reeds whittled into a sharp point at one end. Later, large bird feathers of swans and geese, which are similarly hollow inside, were also whittled and used as pens called quills. Later still, the sharp end was replaced by metal points called nibs that can still be found today on artists' pens and calligraphy pens and on fountain pens. These steel nibs, followed by fountain pens, were introduced in the 1800s and did a better job of holding and distributing the ink mixture, especially the fountain pen since it had a built-in chamber for holding a supply of ink (later, a replaceable cartridge of ink) allowing the pen to become portable and the ink pot to become obsolete.

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violy's profile pic

violy | High School Teacher | (Level 1) Associate Educator

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A mixture can usually be separated back into its original components. When we combine two or more different materials in such a way that no chemical reactions occurs, the resulting substance is called mixture. There are two types of mixture: homogeneous and heterogeneous. 

homogeneous mixture is a mixture where the components that make up the mixture are uniformly distributed throughout the mixture (examples are blood, sea water, mixed drinks, metal alloys, sugar water, the atmosphere, milk, hand cream, smoke, and whipped cream.

heterogeneous mixture is a mixture where the components of the mixture are not uniform or have localized regions with different properties (examples are clam chowder, water and oil, chocolate chip cookies, oil and vinegar, orange juice with pulp, sand water, chicken noodle soup, Trail Mix, soil, and granite. 

We can now say that ink is a mixture. In fact, ink is a homogeneous mixture since its appears to be uniform.

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emildepadua | (Level 1) eNoter

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Before i answer the question let us define what is mixture. Mixture is a combination of two or more substances. It can classified into two, it's either homongeneous and heterogeneous. Ink is considered as a mixture because it contains a lot of compounds like dyes and pigments  and as result is a medium use for writing and for drawing.

 

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