KhanAcademyVideos

Slave Burial Ground, c. 1840s, University of Alabama. A conversation with Dr. Hilary Green, Associate Professor of History and Dr. Beth Harris. For more visit the [Hallowed Grounds Project](https://hgreen.people.ua.edu/hallowed-grounds-project.html)

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Titrating a polyprotic acid with a strong base produces a pH curve with as many equivalence points as there are acidic protons on the acid. The pKₐ values for these protons can be estimated from the corresponding half-equivalence points on the curve, where pH = pKₐ.

Acid–base indicators are compounds that change color when they become protonated or deprotonated. Because this color change occurs over a specific pH range, indicators can be used to approximate the equivalence point of an acid–base titration.

The results of an acid–base titration can be summarized using a titration curve, which plots pH vs. volume of titrant added. For the titration of a strong acid with a strong base, the curve begins acidic and then turns basic after the equivalence point, which occurs at pH = 7. For the titration of a strong base with a strong acid, the curve is similar except that it begins basic and turns acidic.

For the titration of a weak base with a strong acid, the pH curve is initially basic and has an acidic equivalence point (pH < 7). The section of curve between the initial point and the equivalence point is known as the buffer region. At the half-equivalence point, the concentrations of the buffer components are equal, resulting in pH = pKₐ (where pKₐ refers to the conjugate acid of the weak base).

For the titration of a weak acid with a strong base, the pH curve is initially acidic and has a basic equivalence point (pH > 7). The section of curve between the initial point and the equivalence point is known as the buffer region. At the half-equivalence point, the concentrations of the buffer components are equal, resulting in pH = pKₐ.

Sebastián López de Arteaga, Marriage of the Virgin (Los Desposorios de la Virgen), before 1652, oil on canvas, 223.5 x 170 cm (Museo Nacional de Arte, INBA, Mexico City) Additional resources: James Oles, Art and Architecture in Mexico (London: Thames & Hudson, 2013) Painting a New World, exh. cat., ed. Donna Pierce, Denver Art Museum (Austin: University of Texas Press, 2004) (available online) Tesoros, Treasures, Tesouros, the Arts in Latin America, 1492–1820, exhibition catalogue (Philadelphia: Philadelphia Museum of Art, 2006) Kelly Donahue-Wallace, Art and Architecture of Viceregal Latin America, 1521–1821 (Albuquerque: University of New Mexico Press, 2008)

Self-Portrait with Monkey, 1938, by Frida Kahlo is one of the most important works of art in the collection of the Albright-Knox Art Gallery in Buffalo, New York. Kahlo’s art embodies Mexicandad—the unique spirit and quality of being Mexican—combining the country’s indigenous heritage, colonial history and post-revolutionary future. Many of her works and self-portraits are also artistic expressions of the numerous challenges she faced in her lifetime. She was haunted by an unfulfilled desire to have children after surviving a bus accident when she was 18 and looked to her pets, such as her monkey Fulang-Chang, for comfort. She also included them in her works often. Learn more about “Self- Portrait with Monkey,” 1938, with Janne Sirén, the Peggy Pierce Elfvin Director of the Albright-Knox Art Gallery.

A conversation on Monument Avenue, Richmond, Virginia, July, 2021 speakers: Dr. Sarah Beetham and Dr. Steven Zucker

Antonin Mercié, Robert E. Lee Monument, 1890, bronze (removed from Monument Avenue, Richmond Virginia, September 9, 2021) This video was recorded in July 2021. speakers: Dr. Sarah Beetham and Dr. Beth Harris Additional resources Kirk Savage, Monument Wars: Washington, D.C., the National Mall, and the Transformation of the Memorial Landscape (University of California Press, 2011) Kirk Savage, Standing Soldiers, Kneeling Slaves: Race, War, and Monument in Nineteenth-Century America, new ed. (Princeton University Press, 2018) Kevin M. Levin, "Richmond’s Confederate Monuments Were Used to Sell a Segregated Neighborhood," The Atlantic  (Jun 11, 2020)

Wen Zhengming’s Wintry Trees: Mourning and reciprocity from HENI Talks on YouTube. Wintry Trees is a hanging scroll produced by Wen Zhengming at a time of personal loss. Craig Clunas explains some of its classic features and explores the work’s unusual inscription which raises as many questions as it answers. The ‘art market’ of Ming dynasty China was very different from the one we know today. Was Wen Zhengming’s mysterious visitor offering sincere condolences or was his gift-giving merely an attempt to exploit a culture of reciprocity?

A Portrait of Humanity: The Compelling Story of Ayuba Suleiman Diallo from HENI Talks on YouTube. Speaker: Gus Casely-Hayford The life of Ayuba Suleiman Diallo, from modern-day Senegal, reveals some of the startling and uncomfortable truths behind the historic slave trade. Cultural historian Gus Casely-Hayford examines the intriguing portrait of Diallo, which was painted by William Hoare in 1733 and currently hangs in the National Portrait Gallery in London. The depiction of this gentle and educated African Muslim convinced many people in Britain at the time of the inhumanity of slavery. It was an important piece of abolitionist propaganda and reminds us of the complex demography of eighteenth century Britain. Yet Diallo’s life is also one that contains moral contradictions and twists. Where was Diallo from and why does his story matter?

Omar Victor Diop: Black Subjects in the Frame from HENI Talks on YouTube. The relationship between the state and the Black subject is, in many ways, still a highly contested one. What can we draw from historic imagery in order to move forward? In this HENI Talk, Dr Mark Sealy examines Black identity during moments of social upheaval and confrontation, as represented in the oeuvre of artist Omar Victor Diop. In his photographic portraits, Diop uses his own body to restage charged moments in history in a quest for us to look at and learn from these events afresh. His work encourages the viewer to question the narrative of history that we are traditionally taught and see Black people themselves as the agents of change – exploring, for example, the role of Black slaves during the first major revolt in Haiti in the 1790s, or the grassroots dimension of the US civil rights movement in the 1960s, or the often hidden presence of Black women in the history of activism. Press play to hear some of the ways the framing of Black identity through history has hindered, obscured and liberated the lives of many people across the globe.

Building Brasília from HENI Talks on YouTube. 1955. Brazil. A man – Juscelino Kubitschek – campaigning to be president made a promise to the people to construct an entirely new capital city from scratch, to create modern heart for the fledgling country. Kubitschek won; he was elected president and so commenced one of the most ambitious single building projectsever, the city of Brasília fashioned in just 4 years. City planner Lùcio Costa’s graphic design for an ideal city was combined with architect Oscar Niemeyer’s artistic prowess and provocative use of concrete. Niemeyer was notorious for creating pure, sculptural and sometimes shocking buildings. But were these seemingly otherworldly structures practical? And what is their legacy today? Join Professor Richard J. Williams in this HENI Talk to uncover the story of this modernist utopia.

Frederic Edwin Church, Cotopaxi, 1862, oil on canvas, 121.9 x 215.9 cm (Detroit Institute of Arts) A conversation with Dr. Steven Zucker and Dr. Beth Harris

Articles are special adjectives, like "A", "An", and "The". But when do you choose "A", and when do you choose "An"? Let's find out. 

A proton and electron have the same kinetic energy, let's compare their de Broglie wavelength. Next, a proton, and an alpha particle are accelerated through the same potential difference, let's compare their de Broglie wavelength.

Let's explore various graphs of photoelectric experiment, and see how changing intensity and frequency changes the graphs.

When light of frequency 2.42 X 10^15 Hz is incident on a metal surface, the fastest photoelectrons are found to have a kinetic energy of 1.7eV. Find the threshold frequency of the metal. Let's explore how to use Einstein's photoelectric equation to solve such numerical on photoelectric effect.